The resultant force in the vertical direction of the conical pendulum is zero, and the momentum at any moment is mv. In half a period, the direction of the pendulum just reverses, so the change of momentum is 2mv and the impulse is 2MV.

The resultant force on the pendulum ball is the centripetal force, which always points to the O point and the moment is zero. It is also obvious from the figure that the angular momentum is constant.

So the correct option is C.