Answer: C, an apple staying at rest on the ground.
Explanation: When one or more unbalanced forces are acting on an object, it causes change (eg. the apple falling on the ground would be a result of gravity being stronger than the kinetic energy that the tree is putting on the apple). Even in D, the apple is not moving, but the tree branch is still exerting force to keep the apple hanging there.
PS: I studied net forces last year. Hope this helps!
