A parallel plate condenser with a dielectric of dielectric constant $$K$$ between the plates has a capacity $$C$$ and is charged to a potential $$V$$ volts. The dielectric slab is slowly removed from between the plates and then reinserted. The net work done by the system in this process is

A

$$1/2 (K - 1) CV^2$$

B

$$CV^2 (K - 1)/K$$

C

$$(K - 1) CV^2$$

D

zero