Answer:
The correct word that would fit in that sentence is A) estudié.
Step-by-step explanation:
-The sentence using the word estudié:
"Yo estudié en la biblioteca hasta que mis amigos salieron doe la clase."
-The word estudié, means "studied" and that word would fit in the following sentence, because it's saying it past tense.
-The sentence using the word estudio:
"Yo estudio en la biblioteca hasta que mis amigos salieron doe la clase."
-The word estudio, means "study" and that would not fit in the following sentence because it saying right now.