What of the following is a true statement regarding springs? a. in hooke's law, the force exerted by the spring acts in the same direction as displacement. b. springs are designed to provide unpredictable variations in force. c. the force exerted by a spring has a quadratic relationship with the displacement from equilibrium. d. the higher the value of the spring constant, the stiffer the spring. e. the spring constant is represented by the symbol cs