The answer is B. A machine is anything that makes a force bigger in science. So a jack is a machine. All machines has one thing in common: when you put a force to them, they rise its size and apply a greater force somewhere else. For example, using a knife, you can't cut meat with your hand alone, but if you push down on a knife, the long handle and the sharpened blade enlarge the force you apply with your hand—and the meat slices naturally.
