Every college football team -- even those in the Top 25 -- turns over its roster every year with graduations, transfers, etc. So those changes are offseason question marks, especially this time of year.

What's the biggest question for each of the nation's top teams?

The Tigers will be loaded on offense once again with Trevor Lawrence and Travis Etienne returning, but the biggest question in 2020 is also on that side of the ball. Clemson has to replace four starters on the offensive line, including two first-team All-ACC players in right tackle Tremayne Anchrum and left guard John Simpson. With center Sean Pollard and right guard Gage Cervenka also gone, Clemson loses a combined 127 starts among the four players. And that starting group last season was among the best under Clemson coach Dabo Swinney. The good news is the Tigers return left tackle Jackson Carman, a rising star, and have some young talented players on the roster to plug in the holes. -- Andrea Adelson

The Buckeyes made it to the College Football Playoff with a completely balanced team on offense and defense. The offense has quite a few pieces coming back in 2020, including quarterback Justin Fields, but the defense is where there are some big holes that need to be filled. Defensive coordinator Jeff Hafley was hired away by Boston College, and defensive end Chase Young, defensive tackle Davon Hamilton, linebacker Malik Harrison, cornerbacks Jeff Okudah and Damon Arnette, as well as safety Jordan Fuller, are all gone, along with a few others. That is a lot to lose, especially with the rise in nearly every stat since Hafley was hired. If that unit can continue to progress, or at least not regress, Ohio State could have another playoff appearance. -- Tom VanHaaren

Of course the Crimson Tide need a quarterback to replace Tua Tagovailoa. That goes without saying. But perhaps the more pressing question is on the other side of the ball, where coach Nick Saban has to rebuild his defense, which was bitten by the injury bug last season and took a significant step back. It was the reason Alabama lost to LSU and Auburn, not the offense. If middle linebacker and former Butkus Award finalist Dylan Moses can return from injury and stay healthy, he could make a world of difference not just in talent but in leadership. -- Alex Scarborough

Will the offense be as potent as it was a year ago? The Tigers' offensive onslaught in 2019 was nothing short of remarkable, but two of the key pieces who helped supercharge the attack -- quarterback Joe Burrow and passing game coordinator/receivers coach Joe Brady -- are off to the NFL. Myles Brennan appears to be Burrow's likely successor, and how he performs will be a big determining factor in how LSU's offense functions. Brady's role is still to be filled, but the good news for LSU is offensive coordinator Steve Ensminger -- the playcaller during LSU's record-setting run -- is back. -- Sam Khan Jr.

For nearly four full seasons, quarterback was the one position the Ducks didn't have to worry about, thanks to Justin Herbert's extended reign. Due to the nature of the position, his replacement is clearly the most pressing and notable. Tyler Shough, Herbert's primary backup, figures to have the best shot at winning the starting job, but he should get competition from Jay Butterfield, Cale Millen and Robby Ashford. Possibly more important, however, is the state of the offensive line. The Ducks return Outland Trophy winner Penei Sewell, but need to replace the four other starters up front. -- Kyle Bonagura

QB Jamie Newman moves from Wake Forest to Georgia. Rich Graessle/Icon Sportswire

Jake Fromm couldn't drag the Georgia offense out of the dark ages. Come to think of it, neither could a then-true freshman Justin Fields two years ago. But maybe Jamie Newman will do the trick. The Wake Forest transfer is the kind of dual-threat quarterback who might finally force Kirby Smart and his coaching staff to take a second look at transitioning to more wide-open spread concepts. As with LSU a year ago, there's the sense that a more modern offense could be the key to unlocking Georgia's full potential. But as with LSU in the long slog before Joe Brady's arrival, no one is sure when that change will actually happen. -- Scarborough

The Gators dealt with injuries to their best pass-rushers a year ago, Jabari Zuniga and Jonathan Greenard, and that impacted their ability to generate consistent pressure on the quarterback -- especially in their two losses to LSU and Georgia. With Zuniga and Greenard gone, finding those players to wreak havoc in the backfield becomes a top offseason priority. Among the top candidates is Jeremiah Moon, who had a foot injury of his own that held him back last year. Still, Moon was able to get 6.5 tackles for loss. Add in the loss of starting defensive tackle Adam Shuler and the Gators have plenty of questions to answer up front. -- Adelson

How well will the Sooners fill the key veteran losses on defense? Oklahoma's two best defensive players from 2019 -- defensive tackle Neville Gallimore and linebacker Kenneth Murray -- are moving on to the pros after playing huge roles in the Sooners' defensive turnaround. At Gallimore's spot, Perrion Winfrey, the No. 1 player in the ESPN JC 50 whom Oklahoma signed from Iowa Western Community College, could be the successor. There isn't necessarily a clear-cut favorite to replace Murray at middle linebacker, but returnees Levi Draper, Bryan Mead (both of whom backed up Murray) and DaShaun White (who started at weakside linebacker) are among the potential options. -- Khan

It has to be the passing game. New offensive coordinator Kirk Ciarrocca is a run-heavy guy, but his 2019 Minnesota offense thrived because of the level to which the Gophers' incredible wideouts could punish defenders. PSU returns only one wideout who caught more than 12 passes and will need some former blue-chippers (juniors-to-be Jahan Dotson and Daniel George, 2019 signee John Dunmore, 2020 signee KeAndre Lambert) to discover their form quickly. And needless to say, although quarterback Sean Clifford was decent in his first year as a starter, he needs to raise his game as well. -- Bill Connelly

Notre Dame's leading rusher and top three receivers are all gone. Running back Tony Jones Jr., Chase Claypool, Cole Kmet and Chris Finke provided a big portion of the Irish offense last season, so who steps up in their place this coming season? Braden Lenzy has an opportunity to contribute in both the run and passing game, but others are going to have to produce. It helps that quarterback Ian Book is returning to provide some stability, especially because backup Phil Jurkovec transferred to Boston College. Notre Dame added some playmakers in its 2020 recruiting class who might help, including running back Chris Tyree, tight ends Michael Mayer and Kevin Bauman as well as wide receiver Jordan Johnson, which should add options for Book and the offense. -- VanHaaren

Will the offensive line be better? If the Aggies are going to have a breakout 2020 -- which is possible given the schedule -- it has to be. The Aggies gave up the second-most sacks in the SEC last season (34), and they were last in the SEC West in rushing yards before first contact, averaging just 1.76 yards per carry before a defender touched the ball carrier. Texas A&M has a lot of returning talent and a chance to take a big step forward, but the "Maroon Goons" have to step up. -- Khan

Set aside the much-needed development of Bo Nix as a passer for a moment. That's the easy question to get hung up on. But perhaps the more difficult one to answer is how Auburn will rebuild its defensive line, which was arguably the best single unit in college football last season. Derrick Brown was a game-wrecker in the interior and Marlon Davidson was a fearsome pass-rusher, and now they're both gone, along with Nick Coe. Big Kat Bryant is back, which helps, but it's going to take a lot more than that to re-create anything close to the dynamic that Brown and Davidson presented offenses. -- Scarborough

Can the front four deliver? OSU has offensive tools almost everyone else in the country is jealous of. Plus, star linebacker Amen Ogbongbemiga returns, and last season's sophomore-heavy safety corps will now be junior-heavy. But the Pokes didn't get nearly enough push up front -- only one lineman finished with more than five tackles for loss, and OSU didn't generate nearly enough pressure to account for how aggressive they want to be in the back. That simply cannot remain the case. The line has to make everyone else's job easier. -- Connelly

Will the Badgers be able to throw when they need to? With that defense and run game, they don't have to take to the air much, but everyone falls behind schedule, especially against good teams. The receiving corps is going to be ultra-experienced, and you'd think the QB competition between senior-to-be Jack Coan and recent blue-chipper Graham Mertz will be pretty intense. (Coan won the battle this year, but that's not a guarantee he'll do it again.) Will that produce the necessary upgrade? -- Connelly

Who's the next quarterback? With Shea Patterson graduating, Michigan will have a new starting quarterback in 2020. It's probably between Joe Milton and Dylan McCaffrey, but Cade McNamara is also on the roster, trying to compete for his spot. McCaffrey has played the most but has also had his fair share of injuries at Michigan, including a concussion suffered last season against Wisconsin. Milton is somewhat of an unknown because of his limited playing time. He has a cannon for an arm, but is he ready to start? That will all have to get sorted out this offseason as Michigan can't afford another slow start on offense in 2020. -- VanHaaren

The offensive line. In Julian Good-Jones, Collin Olson, Josh Knipfel and Bryce Meeker, ISU has to replace four players who combined for 147 starts up front. The Cyclones already leaned quite pass-heavy in 2019, but without leading receivers Deshaunte Jones and La'Michael Pettway, they could lean on the run more ... if they're able to. Running back Breece Hall should improve, but that won't really matter if he is constantly having to create something from nothing. -- Connelly

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Can Desmond Ridder stay on the field? Ridder is one of the best QBs in the American and plays like a high-usage basketball guard -- the ball's in his hands a lot. He has been credited with 636 passes and 294 rushes in two years. But he was injured in the bowl game against Virginia Tech in 2018, and he labored through injury for most of this past November before missing the first Memphis game. He's going to take a lot of hits, and any chance Cincy has of going 13-0 and beyond requires him in there for every meaningful snap. -- Connelly

The transition from Zak Hill to Eric Kiesau at offensive coordinator should be relatively seamless, considering Kiesau has been on the staff for three years, but the Broncos will head into 2020 hoping for less of a revolving door at quarterback. As a true freshman in 2019, Hank Bachmeier got off to a dream start, but injuries derailed his season and the Broncos ended up starting two others, Jaylon Henderson and Chase Cord, down the stretch. With Henderson gone, Bachmeier probably is the starter, by default, but it's less of a sure thing than it would have felt like three months ago. -- Bonagura

The Golden Gophers have to replace receiver Tyler Johnson, but with quarterback Tanner Morgan, receiver Rashod Bateman, running back Mohamed Ibrahim and the entire offensive line returning, there is a lot of reason for optimism about what they'll look like on offense. The biggest question here is how the change in offensive coordinator will factor in as Mike Sanford comes in to replace Kirk Ciarrocca. As the offensive coordinator at Utah State last season, Sanford guided a unit that could be explosive, at times, but quarterback Jordan Love's numbers took a sharp dive from when he was a sophomore under a different staff. It's a different situation at Minnesota, where he'll join an established staff, so expectations remain very high. -- Bonagura

There are plenty of questions whenever you have a mostly new staff, which Baylor does under new coach Dave Aranda, but the biggest on-field question is how will the Bears replace their stellar 2019 defensive line? The catalyst of the 11-3 season, the Bears' defensive front was nothing short of exceptional, but James Lynch, Bravvion Roy and James Lockhart are now gone. How the Bears go about filling those voids remains to be seen as new defensive coordinator Ron Roberts assesses what he has and how he wants to structure his unit. Getting production even in the ballpark of what those three gave would be huge for Baylor's chances at contending for the Big 12 title again. -- Khan

Has Memphis officially supplanted UCF as the team to beat in the American? Can the Tigers make an undefeated run to the New Year's Six? That's two questions, but they are the biggest facing this program headed into the offseason, especially with former coach Mike Norvell now at Florida State. Memphis put together an all-time great season in 2019, and with 18 starters returning, everything seems to be lining up for another run to the conference championship. Whether this team can deliver with all the heightened expectations and preseason buzz will be fascinating to watch. Especially since UCF is on the regular-season schedule. -- Adelson

The bigger-picture question is whether the Tar Heels can continue their upward trajectory into 2020, when they will more than likely be the favorites to win the Coastal Division. The personnel question centers on the interior of the defensive line, where North Carolina loses starting tackles Aaron Crawford and Jason Strowbridge. The two combined for 95 tackles, 15.5 tackles for loss, 6 sacks and 7 quarterback hurries as the defense showed major improvement in Year 1 under new coordinator Jay Bateman. Crawford and Strowbridge combined for 67 career starts, and UNC is losing veteran experience and a productive presence in the heart of its defense with both departures. -- Adelson

The Hawkeyes are returning quite a bit at running back and at wide receiver, so the question is whether Spencer Petras can step in at quarterback and build on the 10-win season Iowa had in 2019. The pieces are there for Petras, the presumed starter, who is replacing Nate Stanley, with Iowa's top five receivers returning this season. The roster could also get a boost from wide receiver transfers Oliver Martin and Charlie Jones, as well as a more seasoned Sam LaPorta at tight end. Petras threw only 10 passes last season, though, so it's unknown what he is capable of and how he can lead this offense. If he steps in and produces early, Iowa could be in store for a great season. -- VanHaaren

Will Tom Herman's massive staff turnover work out? The talent isn't really much of an issue at Texas; the Longhorns have recruited well since Herman's arrival. But an 8-5 season was underwhelming, and as a result, Herman fired both coordinators and brought in Mike Yurcich to run the offense and Chris Ash to run the defense, as well as a host of new position coaches. How quickly the staff jells and how well the players take to the new staff will be key as the Longhorns embark on a pivotal 2020 campaign. -- Khan

Let's suppose that the defense continues to improve and quarterback Jarrett Guarantano turns a corner as a fifth-year senior. Trey Smith is coming back, so the offensive line should be in good shape. The running game should be as well with Eric Gray and Ty Chandler expected back. What does that leave? Pass-catchers. That's the 18-wheeler-sized hole on offense with Jauan Jennings, Marquez Callaway and Dominick Wood-Anderson all moving on. The trio caught 110 of the 200 passes the Vols completed last season, and outside of Josh Palmer, there's not a lot of experienced players to replace them. -- Scarborough