Abner tells a representative of Brass & Woodwind Musical Instruments, Inc., that he will pay for Claudia’s trumpet if she does not. Abner does not secure any personal benefit for this promise. This promise is enforceable as a contract:.
a. under any circumstances.
b. only if it is in writing.
c. only if the value of the trumpet is more than $500.
d. only if Claudia agrees to it.

The correct option is B,only if it is in writing.

Explanation:

Such promise is not enforceable since one of key elements of enforceable agreement(contract) is missing.

The missing element is that Abner is not getting anything of value in return for the promise to pay for Claudia's trumpet.

The only way to get Abner to fulfill the promise in law parlance is get the promise documented as well as signed by Abner,that can be used as an evidence against Abner in future in order to ensure the promise is fulfilled.

Option B

If only it is in writing

Explanation:

At this point in time, Abner is opting to act as a surety for Claudia. and surety contracts are legally binding, once they are signed.

Claudia already owes Brass & Woodwind Musical Instruments, Inc and there is a contract already existing between the two parties. for Abner to decide to pay Claudia's fee, it means that Abner wants to act as surety for Claudia.

However, surety contracts need to be written down and signed for them to be effective. This makes option B the correct answer