What causes the restoring force in a simple pendulum?

Question

A. friction between the thread and the support

B. the force exerted on the pendulum bob while displacing it from the mean position

C. the component of the weight of the bob acting perpendicular to the thread

D. the component of the weight of the bob acting parallel to the thread

Answer 1

gravity wants to make the pendenlum bob fall, the restoring force is the force exerting on the bob while it is displaced from the mean position.