simple harmonic motion of a spring

Question

An object swinging on the end of a string forms a simple pendulum. Some students often cite the simple pendulum's motion as an example of SHM. That is not quite accurate because the motion is really

A:      approximately SHM only or small amplitudes.

B:      exactly SHM only for amplitudes that are smaller than a certain value.

C:      approximately SHM for all amplitudes.

D:      Don't know.