Answer:
The answer for the question is:
- Los ojos de mi amigo son azules.
Step-by-step explanation:
In Spanish, different to the English, the adjectives have plural form, then, when the substantive has the plural form, the adjective must has it too, in the sentence you have written: "My friend's eyes are...", with eyes that are a plural noun, next to must be assigned an adjective, in this case, the one adjective that is in plural form is "azules", the others are in singular form.