Which of the Following Transfers Is Taxable Under the Gift

Which of the following transfers is taxable under the gift tax statutes?

A) Mark sold land to an unrelated party for less than its fair market value because he needed cash in a hurry.
B) After a friend's death, Sharron wrote a check to the university to pay the college tuition for the friend's son.
C) Marilynn wrote checks to the landlord to pay her aunt's rent for ten months when her aunt was unemployed.
D) Jose wrote a check to the doctor to pay a friend's medical bill when he had surgery.