Bob wants to help his daughter, Violet, upgrade her home. Bob buys a new refrigerator and oven for Violet on credit from a home supply store. He instructs the home supply store to deliver the new appliances to Violet's home for installation. Which of the following is true with regard to this scenario? 

a. Bob's promise to pay the home supply store must be in writing. 

b. Bob's promise to pay the home supply store can be oral. 

c. Bob's liability to the home supply store is quasi-contractual in nature. 

d. Bob's promise to pay the home supply store is void.