When is the guarantor liable for the obligation of the debtor?

• A. Once the obligation becomes due and demandable;
• B. Only after judgment is obtained against the principal debtor and he is unable to pay; (Baylon v. CA, August 17, 1999)
• C. The moment the judgment against the debtor becomes final and executory;
• D. Once demand is made for both the debtor and guarantor to pay.