A block with mass m is at the top of a smooth inclined plane with an angle of inclination \beta. The block is then released from rest and reaches the bottom of the inclined plane at a velocity v_f. If the air resistance is neglected, the acceleration due to gravity is g and the length of the side of the plane is L, the work done by the gravitational force on the block is
a. mgL
b. mgL\cos cos\beta
c. 0
d. \frac{1}{2}m{v_f}^2
e. \frac{1}{2}m{v_f}^2 - mgL\sin sin\beta