The x–t graph of a particle performing simple harmonic motion is shown in the figure. The acceleration of the particle at $t=2\ s$ is:

A $-\frac{\pi^2}{16}\ ms^{-2}$
B $\frac{\pi^2}{8}\ ms^{-2}$
C $-\frac{\pi^2}{8}\ ms^{-2}$
D $\frac{\pi^2}{16}\ ms^{-2}$