Right answer:
Correct
This sentence is given in the imperfect tense. This tense is used to talk about past actions, conditions, or events that occurred regularly or frequently or that were in progress in a moment in the past. Here we use the verb ser conjugated as era that stands for the third person singular. Also, this sentence stands for superlatives. The superlative is a form of an adjective that expresses the highest possible amount of something talking about what is the most or the least. So:
IN SPANISH:
El capitán era el más feliz
IN ENGLISH:
The captain was the happiest
