The correct answer is A.
A subject - verb agreement means that the subject and the verb of the sentence must be in agreement in number.
With indefinite pronouns ( each, everybody, nobody etc.), the rule is that they are always followed by a verb in singular.
Example: Everyone is wearing black.
Each volunteer and staff member needs to arrive at a scheduled time.
Each is singular because it refers to the subject being singular: each volunteer and each staff member.
