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. zero
B. `1/2(K-1)CV^(2)`
C. `(CV^(2)(K-1))/(K)`
D. `(K-1)CV^(2)`
