Which one of the following equations of motion represents simple harmonic motion?

The defining characteristic of Simple Harmonic Motion (SHM) is that the acceleration of the particle is directly proportional to its displacement from the mean position and is directed towards the mean position.The mathematical form is:
$$a=-{\omega }^{2}X$$
where $X$ is the displacement from the equilibrium point.In option A, $a=-k(x+a)$. If we substitute $X=x+a$ (where $X$ is the displacement from the equilibrium point at $x=-a$), then $a=-kX$, which is the standard SHM equation.