A box with weight $W$ is drawn up a slope by a force $P$. The slope has length $d$, and the box gains a vertical height of $h$. The frictional force acting between the box and the slope is $F$. The diagram indicates the directions of the forces. The slope is used to lift the box vertically. Which expression represents the efficiency of the slope?
- A$\frac{Fd}{Wh}$
- B$\frac{Pd}{Wh}$
- C$\frac{Wh}{Fd}$
- D$\frac{Wh}{Pd}$