Assertion (A): When a person walks forward on a level road while steadily carrying a suitcase, he does no mechanical work on the suitcase.
Reason (R): The force exerted by the person on the suitcase is vertical whereas the displacement of the suitcase is horizontal.
a) Both A and R are true, but R is not the correct explanation of A
b) A is false, but R is true
c) Both A and R are true, and R is the correct explanation of A
d) A is true, but R is false