What Is the Crucial Difference Between an S^D and a Warning

What is the crucial difference between an S^D and a warning stimulus?

A) The presence of an S^D means that if the response does not occur, the aversive outcome will occur. The presence of a warning stimulus means that a specific outcome may occur only if the response occurs.
B) The presence of a warning stimulus means that if the response does not occur, the aversive outcome will occur. The presence of an S^D means that a specific outcome may occur only if the response does occur.
C) The S^D is removed contingent on the response, whereas the warning stimulus remains in place regardless of whether the response has occurred.
D) A & C
E) Are you serious!? They have nothing in common.