Answer
Choice A.
Work Step by Step
The velocity of the crate is constant, so the net force is zero, and the net (total) work done on the crate is zero.
The normal force is perpendicular to the velocity and does no work.
The force of friction opposes the direction of motion and does negative work.
Your pushing force and the downhill component of gravity point in the direction of motion, and each do positive work.
Because the total work is zero, the work done by friction cancels the positive work done by gravity and by you, so friction does the greatest magnitude of work on the crate.
