Question

buenos días, señor díaz. ¿cómo está ________?
a. usted
b. tú
c. amigo
d. tarea

Explanation:

The sentence uses formal address ("señor Díaz" and the formal verb form "está"), so the formal second-person pronoun is required. Option A is the formal singular "you" matching the context; B is informal, C means "friend", D means "homework" which do not fit.

Answer:

A. usted