When at rest, a liquid stands at the same level in the tubes shown in figure. But as indicated a height difference $h$ occurs when the system is given an acceleration a towards the right. Here, $h$ is equal to
(a) $\frac{a L}{2 g}$
(b) $\frac{g L}{2 a}$
(c) $\frac{g L}{a}$
(d) $\frac{a L}{g}$