Fill in the blank (12) with the most appropriate word.
A verb is used to express an occurrence, action, or state. It is the grammatical centre of the predicate in a sentence.
An auxiliary verb is a verb which gives is used in the formation of tenses, moods, tones, etc.
Option A is correct as we are talking about Enrique having studied medicine because he wanted to become a doctor. (simple past tense)
The other options are wrong as no other tense other than past simple tense can be used.
The correct answer is A) studied