Final answer:
The correct tense to complete the sentence is 'era' as 'Yo' is the first person singular pronoun in Spanish and 'era' is the imperfect tense conjugation of the verb 'ser' (to be).
Step-by-step explanation:
The correct tense to complete the sentence is era, as 'Yo' is the first person singular pronoun in Spanish and 'era' is the imperfect tense conjugation of the verb 'ser' (to be).
Learn more about Tense conjugation of the verb 'ser' in Spanish