Answer: a. Yo estoy ocupado.
Step-by-step explanation:
¿Cómo estás tú?: How are you?
A: Yo estoy ocupado: I'm busy. ==> Valid answer since you answer how you feel when being asked about you.
B: Nosotros estamos emocionados.: We are excited ==> The question asks about you and you only, not anyone else.
C: María está nerviosa: Maria is nervous. ==> The question didn't ask about María.
D: Roberto está aburrido.: Robert is bored. ==> The question didn't ask about Roberto.
Answer: A