Yo _________ en el coro.
Translation:
I [blank] in the choir. (Coro also means "chorus", but clearly "choir" is the definition being used here.)
One sings in a choir. The infinitive for "to sing" in Spanish is cantar; this must be conjugated for our verb. The verb is yo, which is first-person singular. The conjugation is canto.
Answer:
canto
Yo canto en el coro.
