Concept:
In Simple Harmonic Motion, acceleration is proportional to displacement and is directed towards the mean position.
\[
a=-\omega^2x
\]
The negative sign indicates direction only.
Step 1: Convert displacement into SI unit.
\[
x=4\,\text{cm}=0.04\,\text{m}
\]
\[
\omega=0.5\,\text{rad/s}
\]
Step 2: Apply SHM acceleration formula.
\[
a=\omega^2x
\]
\[
a=(0.5)^2(0.04)
\]
\[
a=0.25\times0.04
\]
\[
a=0.01\,\text{m/s}^2
\]
Thus,
\[
\boxed{a=0.01\,\text{m/s}^2}
\]
Hence the correct answer is
\[
\boxed{(C)}
\]