The answer would be:
Pulling a trailer up a hill
Here is why:
In physics, work is computed by the formula:
W = Fd or F(cosΘ)d
Where: F = Force applied on the object
d =displacement
So in order for work to be done, the object needs to be displaced. In the case of the trailer, the trailer is being pulled and it is travelling in the direction of the force applied.
The other options the object is not displaced. Even if you exert a force, if the displacement remains the same, then it will always be zero, so the force times displacement will be 0, hence no work is done.
