Right answer:
a. miembro
The word miembro means member is someone who belongs to a group or an organization. So Daniel is a member of the French Club. We use the verb ser here conjugated as es that is the conjugation of this verb for the third person singular in the simple present. On the other hand, since Daniel is a masculine noun, we use the indefinite article un that matches this form. Finally:
Daniel es un miembro del Club de francés