A block of mass m is directly pulled up slowly on a smooth inclined plane of height h and inclination θ with the help of a string parallel to the incline. Which of the following statement is incorrect for the block when it moves up from the bottom to the top of the incline?
a. Work done by the normal reaction force is zero
b. Work done by the string is mgh
c. Work done by gravity is mgh
d. Net work done on the block is zero