Facebook CEO Mark Zuckerberg sat through five hours of testimony in a joint session with two Senate committees on Tuesday, and he'll sit in front of the House Committee on Energy and Commerce on Wednesday.

Zuckerberg is facing questions about Facebook's involvement in various data-privacy scandals and how it can address those issues.

Zuckerberg's team has been preparing him for the hearings for weeks, but he was unable to answer several of the questions on the spot.

In the span of two days, Facebook CEO Mark Zuckerberg answered questions from 44 senators from two committees and 55 representatives on the House Committee on Energy and Commerce in two separate hearings that went for nearly five hours each.

He was answering questions about the role Facebook played in various data-privacy scandals and how it can address those issues.

Zuckerberg had been training for weeks to face the three congressional committees, but his talking points didn't prepare him to answer every question that came his way — some required specific figures or precise explanations that he wasn't able to provide on the spot.

Even when prodded, Zuckerberg was careful not to promise a response, addressing questions he was unsure of with some variation of "If you'd like, I can have my team follow up with you after this."

Here are some things Zuckerberg's team will need to come back to senators with:

A list of applications that Facebook has previously banned because data was transferred in violation of Facebook's terms. Sen. Chuck Grassley

The number of audits Facebook has conducted to ensure deletion of improperly transferred data, or "anything about the specific past stats, that would be interesting." Sen. Chuck Grassley

The number of accounts linked to the Internet Research Agency, a pro-Kremlin propaganda group, that Facebook has taken down. Sen. Dianne Feinstein

Whether any Facebook employees worked with Cambridge Analytica while the data analytics company was working with Donald Trump's 2016 presidential campaign. Sen. Maria Cantwell

Whether the feature for adults using Facebook Messenger on Android to opt into using the app in combination with messaging and allow Facebook to collect data about their calls or texts also applies to minors. Sen. Roger Wicker

Whether Facebook tracks a user's internet-browsing activity after they have logged off Facebook's platform — and if so, a detailed explanation of how. Zuckerberg said that Facebook uses cookies for security and ad-measuring purposes but that he wanted "to be precise" in his full response. Sen. Roger Wicker

How Facebook discloses to its users the tracking practices that take place after users log off. Sen. Roger Wicker

Whether the specific "unverified divisive pages" on Facebook that Leahy displayed during the testimony were created by Russians. Sen. Patrick Leahy

A breakdown by state of the 87 million profiles Facebook estimates to have had data swept up in the Cambridge Analytica scandal. Sens. Amy Klobuchar and Dean Heller (Heller asked for Nevada specifically)

Whether there's overlap between the 126 million users who may have seen content shared by Facebook groups associated with the Internet Research Agency and the 87 million who may have been affected by the Cambridge Analytica scandal. Zuckerberg said that an investigation was underway and that Facebook thinks it's possible there could be a connection. Sen. Amy Klobuchar

Whether it's possible that the data Cambridge Analytica stored is in Russia. Sen. Amy Klobuchar

An explanation of how Facebook treats data on devices not logged into it. Sen. Roy Blunt

Whether Facebook's "bug bounty" program will address impermissible sharing of information and not just unauthorized access to it. Sen. Jerry Moran

Why Facebook moved for the dismissal of a discrimination lawsuit against it that argued that its tools allowed advertisers to not target certain groups, including people of color, for some housing and employment opportunities. Sen. Cory Booker

How long Facebook keeps a user's data after they delete their Facebook or Instagram account and whether that data can sit in backup copies. Sens. Dean Heller and Cory Gardner

A breakdown of the principles Facebook will use to guide the development of artificial-intelligence practices, as well as details about those practices and how they could help users. Sen. Gary Peters

A list of the firms other than Cambridge Analytica that received the Facebook user data Aleksandr Kogan collected. Zuckerberg identified Eunoia but said there may have been a couple of others. Zuck told Congress that he doesn't believe there's a large number of them. Sen. Tammy Baldwin and Rep. Jan Schakowsky

More information about how Facebook is accounting for organizations based outside the US when providing transparency about political ads. Sen. Tammy Baldwin

Whether the government or federal officials can track what a person's doing, with or without a warrant, on the social network. Sen. Cory Gardner

Follow-up on a case in which a former state representative's announcement that he was running for state senate was rejected for not following Facebook's advertising policies. Rep. Fred Upton

Whether Facebook will give consumers in the US the same right to object to using their data for marketing purposes the way that EU users under GDPR will get, and how Facebook plans to implement that. Rep. Michael Burgess, Rep. Jan Schakowsky, and Rep. Peter Welch

Whether the data that's mined for security purposes is also used to sell as part of the business model. Zuckerberg said he believes that they collect different data for those but wasn't sure. Rep. Steve Scalise

Whether someone was held accountable for the Diamond and Silk "mistake," as Zuckerberg referred to it. The CEO was in D.C. preparing to testify when this developed. Rep. Steve Scalise

If there was a bias implemented in the Facebook algorithm when it was developed (the Congressman showed a chart that showed bias against conservative content and favorable bias towards liberal content) and what's being done about it. Zuck said there was no directive to do so and would look into how that happened. Rep. Steve Scalise

Whether the data held by derivatives of the firms obtained data from Alexandr Kogan was also deleted. Rep. Jan Schakowsky

The initial offer terms and any subsequent offer terms that Facebook presented to each candidate (Clinton and Trump) for sales support — the congressman referred to them as campaign embeds — for the 2016 election. Rep. John Sarbanes

Facebook information that has been shared with Russia in the past, if any. Zuckerberg said Facebook cooperates with any "valid law enforcement requests" from different countries, but he wasn't aware of any data had been shared with Russia specifically. Rep. Adam Kinzinger

Number of data points that Facebook has for the average non-user. Rep. Ray Luján

If the employee(s) at Facebook who took down an ad for Franciscan University and put it up again only after the media got involved was/were held accountable. Rep. Bill Johnson

What Europe got wrong with GDPR — Zuckerberg was only able to provide a response to what he thinks they got right. Rep. Scott Peters

The number of Facebook Like buttons, Facebook Share buttons, and "chunks of Facebook Pixel code" there are on non-Facebook webpages. Rep. Debbie Dingell

How limiting Facebook's use of data may actually prevent innovation and the positive social change that Facebook wants to promote. Rep. Ryan Costello

In addition to statistics and explanations, Zuckerberg told a few senators and representatives that his team would circle back to conversations about data-privacy legislation like the Honest Ads Act (Klobuchar), the My Data Act (Sen. Richard Blumenthal), the Consent Act (Sen. Ed Markey), the Broswer Act (Rep. Marsha Blackburn and Rep. Leonard Lance), and the Secure and Protect Americans' Data Act (Rep. Jan Schakowsky).

Sen. Thom Tillis asked that during Facebook's investigation Zuckerberg go back to "the first known high-profile national campaign that exploited Facebook data," but didn't require him to follow up.

Others requested future discussions on the following:

Submitting regulation proposals to prevent a monopoly in the industry, though exactly which industry was unclear. Sen. Lindsey Graham

The possibility of implementing a 72-hour rule to notify users of a data breach. Sen. Amy Klobuchar

The details of allowing civil-rights organizations to audit the companies dealing in areas of credit and housing. Sen. Cory Booker

Whether there should be financial penalties when large data providers like Facebook are breached. Sen. Maggie Hassan

Sending a Facebook representative to a meeting of chief executives and senior leaders to discuss the sale of illegal drugs online. Sen. Shelley Moore Capito and Rep. Buddy Carter

Sharing information on Facebook's plans to spread Internet connectivity in rural areas. Sen. Shelley Moore Captio, Rep. Morgan Griffith, Rep. Bill Johnson, Rep. Dave Loebsack.

Legislation that unequivocally says users own their data and that makes a "stronger affirmative opt-in requirement" for Facebook. Sen. Todd Young

Making a commitment to change all the user default settings to minimize the collection and use of user data. Rep. Frank Pallone

Changing Facebook's business model in the interest of user privacy. Rep. Anna Eshoo

Personally convening a meeting of CEOs in the tech sector to develop a strategy to increase racial diversity in the industry. Rep. G. K. Butterfield

Providing numbers on Facebook's retention for its employees, broken down by race, to be included in Facebook's diversity update starting this year. Rep. G. K. Butterfield

Whether consumers should be able to correct or delete inaccurate personal data that companies have gathered on them. Rep. Peter Welch

National security concerns that would stem from access to information like the geographical location of members of the armed services. Rep. Richard Hudson

Sending a Facebook representative to meet with the FDA commissioner and CEOs of internet companies to address the problem of online drug commerce. Rep. Buddy Carter

The record will be open for 14 days after the Senate hearing and for 10 days after the House hearing, meaning senators and representatives will still be able to submit written questions. Zuckerberg can make corrections to his testimony during this time too.

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