Which of the following involves a non-zero net force?

I. A hockey-puck sliding at a constant speed on ice.
II. The earth revolving around the sun at a constant speed.
III. An object falling near the surface of the earth.

A) I only
B) III only
C) Both I and II
D) Both II and III
E) None of the above

Okay so I know that if there is a non-zero force, there has to be an acceleration. I put B, but I got it wrong. Please help me! Thanks in advance!