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J, 10 bytes

#'\/'{~2|]

This is a six-train verb, consisting of:

# ('\/' {~ 2 | ])

This is a hook between # and ('\/' {~ 2 | ]) ; a hook (f g) y expands to y f (g y) , so this expands to y # (... y) , which, for single-characters, yields a list of y characters.

The second part is a 5-train, consisting of:

'\/' {~ 2 | ]

This evaluates to two forks:

'\/' {~ (2 | ])

The inner fork, 2 | ] , is modulus two. The outer fork, therefore, is:

'\/' {~ mod2

Which takes ( {~ ) the mod2 index ( mod2 ) from the string / .

Then, using the hook from above:

y # (apt char)

This yields what we want, and we are done.