ay, julio, estás muy pálido. ¿quieres sentarte en una

Since before the blank we have the indefinite article that matches the feminine singular form, then we must choose a feminine singular noun. In this way, the more logical noun that matches this sentence is silla because it's a feminine singular noun that translates into chair. So, we can write this sentence as follows:

Ay, Julio, estás muy pálido. ¿Quieres sentarte en una silla?

the answer is c. estudió

explanation:

to translate: last year a group from my school went to cuba and studied the history of the island. you would use preterite form because it was one time and they use fue in the sentence.