Which events triggers the subsequent steps of excitation-contraction coupling?

Can someone explain to me how to do this problem ?

How does the image distance (di) of a convex lens compare with the image distance of a concave lens? a. the image distance of the convex lens is positive, and that of the concave lens is negative. b. both are negative for a virtual image. c. both are positive for a virtual image d. the image distance of the convex lens is negative, and that of the concave lens is positive.

Chemical energy is a form of energy. a. heat b. kinetic c. potential d. electromagnetic