Lloyd’s roommate, Don, classically conditioned Lloyd to cringe whenever Don opened a squeaky drawer by pairing a squeak with a ping pong ball to Lloyd’s head. Lloyd wants to return the favor, so when Don is out, Lloyd discretely wires an electrode to the drawer handle to Don will be shocked when he touches it. Lloyd is using ____

a. ​negative reinforcement
b. ​positive reinforcement
c. ​negative punishment
d. ​positive punishment