Brick and carmen are in an auto accident. brick offers carmen $2,000 if she promises not to pursue her potential legal claim against brick. carmen agrees. later, carmen discovers that it will cost $1,500 to repair her car and $4,000 to cover the medical expenses for a latent injury. the agreement between brick and carmen

a. a release.
b. a covenant not to sue.
c. promissory estoppel.
d. an illusory promise.