The piston is now pulled out slowly and held at a distance 2L from the top. The pressure in the cylinder between its top and the piston will then be

A

$$P_0$$

B

$$\frac{P_0}{2}$$

C

$$\frac{P_0}{2} + \frac{Mg}{\pi R^2}$$

D

$$\frac{P_0}{2} - \frac{Mg}{\pi R^2}$$