According to Hookes Law, in order for a spring to apply a restorative force, what must be true about the displacement of the spring? a. The displacement must be proportional to the spring constant b. The displacement must be towards the spring, to compress it and cause it to force back c. The displacement must be measured away from a starting rest position in order to have a force from the spring d. The displacement must be away from the spring, to stretch it and cause it to pull back