[Solution by Dr. Abubacker] $x=\frac{x_0}2(1-\cos t)$ is SHM about $x=\frac12$ with amplitude $\frac12$. $K=\frac12m\omega^2\left[\frac14-\left(x-\frac12\right)^2\right]$, an inverted parabola that is zero at $x=0$ and $x=1$ with maximum at $x=\frac12$. This is option (4). Answer (4).