Los ojos de mi amigo son ___________.
Translation:
My friend's eyes are [blank].
The options are as follows.
A. verde - green (singular)
B. gris - grey (singular)
C. azules - blue (plural)
D. café - brown (singular) (also translates to coffee)
The subject is plural (Los ojos), thus the adjective must also be plural.
Answer:
C. azules