Yo- é
tú- aste
él/ella/ud.- ó
nosotros- amos
vosotros- asteis
ellos/ellas/uds.- aron
Answer: ¿Nadas tú?
But the correct way would be
¿Tú nadas?
Cantaba is the correct imperfect tense for the word in parentheses.
The translation is “After eating tamales my friends sang(cantaba) a lot” Cantar means to sing and cantaba means “sang”. Sang makes it past tense, so it makes more sense in the sentence as well.
Hopefully this helped :)