The Guarantor Paid the Obligation of the Debtor When Demand

The guarantor paid the obligation of the debtor when demand is made. Can he ask for reimbursement?

A) No, because he is a voluntary payor.
B) No, because judgment has yet to be obtained against the debtor.
C) No, because he has not been able to exercise the benefit of excussion.
D) Yes, because the benefit of excussion is a right granted to him which can be waived.