<span>¿Qué son Buenos Aires y Barcelona? is all that i can find out i hope this helps a little.</span>
Answer:
The answer is clearly option a) "eras"
Explanation:
Since it keeps the verb in the past
- Servir ⇝ Sirva

You only have to remove the <u>direct object</u> that is added to the verb. The verb must not have the direct object.
<h3><em><u>MissSpanish</u></em></h3>