One end of a light spring of spring constant k is fixed to a wall and the other end is tied to a block placed on a smooth horizontal surface. In a displacement, the work done by the spring is +(21)kx2 . The possible cases are
a. The spring was initially compressed by a distance x and was finally in its natural length
b. It was initially stretched by a distance x and finally was in its natural length
c. It was initially in its natural length and finally in a compressed position
d. It was initially in its natural length and finally in a stretched position