Which of the Following Would Be Unenforceable Because the Subject

Which of the following would be unenforceable because the subject matter is illegal?

A) An employer promises not to press charges against her employee for embezzlement because the employee agreed to make restitution.
B) An attorney charges a fee to represent a client in a civil court action.
C) A restrictive covenant in an employment contract prohibiting a former employee from using the original employer's trade secrets at his or her new job.
D) An agreement to pay an expert in a particular field to present a case to a legislative body seeking favorable legislation but leaving it up to the legislative body to decide on the issue.