A crate rests on a rough floor. Using a rope attached to the crate, a man applies a force which is insufficient to move it. What could be the reason?
A) The friction between the crate and the floor is too high.
B) The force applied by the man is greater than the force of static friction.
C) The crate is too heavy for the man to move.
D) The floor is too rough for the crate to slide easily.