A capacitor consists of two parallel metal plates of area `A` separated by a distance `d`. A dielectric slab of area `A`, thickness `b` and dielectric constant `k` is placed inside the capacitor. If `C_(k)` is the capacitance of capacitor with dielectric, under what limits the values of `k` and `b` are to be restricted so that`C_(k)=2C`, where `C` is capacitance without dielectric?
A. `k=(4b)/(2b-d)` & `d/3 lt b le d`
B. `k=(2b)/(2b-d)` & `d/2 lt b le d`
C. `k=(2b)/(2b-d)` & `d/2 le b le 2d`
D. `k=(2b)/(2b-d)` & `d/4lebled`
