Let us consider a spring-mass system. When the spring is being stretched or shortened, the spring force acting on the mass is in a direction that is opposite to the direction of the displacement of the mass and so the work done by it is negative. On the other hand, as the spring returns to its equilibrium position, from a state of extension or compression, the spring force acting on the mass is in the direction of displacement of the mass and so the work done by it is positive. Spring force is the force that try to restore the original shape of the spring. When you stretch a spring you change it's configuration. And trust me spring doesn't like that. How do I know that the spring doesn't like that? That's because as soon as you will remove the force that you are applying on the spring the spring will immediately try to regain it's original shape. For the time when you were stretching or contacting the spring you were making spring attain a configuration that wasn't its original configuration. You had to apply force to change it's shape because spring force was opposing your action. So for that time interval spring force is in opposite directions to displacement -the work done by spring force is negative. That work done is said to stored providing spring potential energy. As soon as you leave the spring, the spring moves back towards 0 position that's when the spring force is doing positive work. Force and displacement have same direction. So it depends on the situation. If you have a spring and wish to stretch it further, you have to exert a force in a direction opposite to the spring force and hence in the same direction as the extension, so you are doing work on the spring. On the other hand, if a stretched or compressed spring returns to its equilibrium length, then work is done by the spring, which is positive meaning b. False is the answer because the positive or negative varies on the situation.