The variation of displacement with time of a simple harmonic motion $(SHM)$ for a particle of mass $m$ is represented by $y = 2 \sin \left(\frac{\pi t}{2} + \phi\right) \text{ cm}$. The maximum acceleration of the particle is

• A
  $\frac{\pi}{2} \text{ cm/s}^2$
• B
  $\frac{\pi}{2m} \text{ cm/s}^2$
• C
  $\frac{\pi^2}{2m} \text{ cm/s}^2$
• D
  $\frac{\pi^2}{2} \text{ cm/s}^2$