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 volt. 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
