Which one of the following is true about a firm commitment? Select one: a. A firm commitment is a transaction that has already occurred and the commitment to pay or receive payment is pending. b. A firm commitment is an agreement with legally enforceable terms c. A firm commitment is a contract that allows both the buyer or seller an option to engage (or not) in a long-term transaction. d. A firm commitment occurs as a result of a historical relationship and there is an expected commitment to engage in a transaction in the future