A metal block is sliding along an infinite, frictionless, horizontal plane. There are only two forces acting on the metal block: gravity and an upward force from the plane. Which of the following best describes the metal block's motion?

A.

The metal block will eventually slow down and stop.

B.

The upward force will accelerate the metal block forward.

C.

Gravity will accelerate the metal block downward.

D.

The metal block will move at the same speed forever