There's no suggestion of an attack on Martin's behavior. No one is accusing Martin of improperly issuing trip invitations. (A) just doesn't describe the argument.

Whether or nor Martin can afford this trip is beside the point. We need to attack the argument's reasoning on the topic of Jerome giving a false excuse, and (B) doesn't do that.

Jerome's vacation preferences aren't relevant unless we assume that cost isn't truly his reason for refusing this trip, which would mean we already accept the conclusion. But the flaw is present before we even get that far: there's no reason to think cost isn't the real issue.

(D) has one major problem: we don't know if Jerome has other reasons to refuse. It's only the argument's conclusion that implies Jerome has another reason, but there's no premise telling us for sure. As far as we know, cost could truly be Jerome's only reason.

If there were a premise which concretely presented another reason, then (D) could be correct. But the argument's only premise is that Jerome has repeatedly given the same excuse, which just doesn't indicate that the excuse is false.

In other words, the argument doesn't consider that cost could be the true reason. This accurately identifies the flaw: Jerome could just give the same excuse multiple times because it's true. Because the argument doesn't consider this possibility, it can't convince us that the excuse is really false.