On Saturday, Rob offered to sell his private jet to Gamino. Gamino was interested but needed some time to secure financing from his bank. Gamino asked Rob if he could have until Tuesday to give his answer, and Rob agreed. On Sunday, Rob offered to sell his private jet to Ivy. Ivy offered Rob $150 to keep his offer open to her until Monday, and Rob accepted this offer. The very next day, on Monday, Ivy accepted Rob's offer to sell his private jet to her. Rob then called Gamino to tell him that he could no longer sell him the private jet. Which of the following statements is TRUE?

a. Rob is liable to Gamino under these circumstances, and he acted unethically.

b. Rob and Ivy have a binding contract and Rob will be liable to Ivy if he refuses to sell her the private jet.

c. Since Rob's offer to Gamino was firm, Ivy is liable to Gamino for direct inducement to breach of contract.

d. Both (a) and (b) are true.

e. Both (b) and (c) are true.

f. (a), (b) and (c) are true.

What should be the answer of this question and what are the legal rules and facts supporting the answer.