Answer:
See explanation for answer.
Step-by-step explanation:
Mis amigas son buenas.
The correct is, "amigas" to this question. It is, "amigas" ( option b ) and not "amigos" because "buenas" is the femine version of "buenos". "Amigas" means "friends" in English. Except all those friends are girls.
I hope this helps!
Have a lovely day!