A person of mass $M$ is sitting on a swing of length $L$ and swinging with an angular amplitude $\theta_0$. If the person stands up when the swing passes through its lowest point, the work done by him, assuming that his centre of mass moves by a distance $l$ ($l \ll L$), is close to:
(1) $Mgl\left(1 - \theta_0^2\right)$
(2) $Mgl\left(1 + \frac{\theta_0^2}{2}\right)$
(3) $Mgl$
(4) $Mgl\left(1 + \theta_0^2\right)$