In Which of the Following Situations Is There Adequate Consideration

In which of the following situations is there adequate consideration on the part of the promisor to support enforcement of a contract?

A) Bob,a police officer,promises to drive by your house and check on it during his off-duty time.
B) Sam,a first-grade teacher,promises to make sure your child learns his lessons in class for $500.
C) LBM Corporation,at Fred's retirement dinner,promises to pay Fred $2,000 a month during his retirement because of his years of dedication to the company.
D) I promise to buy a bike from you for $400 if I decide I'm going to get a new bike this year.
E) Billy,because of all that his mother did in raising him,promises her that he will buy her a new car.