A mass $M$ is performing linear simple harmonic motion, then correct graph for acceleration $a$ and corresponding linear velocity $v$ is

The displacement of a particle varies according to the relation $x=4(\cos \pi t+\sin \pi t)$. The amplitude of the particle is

The $x-t$ graph of a particle undergoing simple harmonic motion is shown below. The acceleration of the particle at $t=\frac{4}{3} \mathrm{s}$ is