Select correct statements
(a) charge cannot be isolated
(b) Repulsion is the sure test to know the presence of charge
( c) Waxed paper is dielectric in paper capacitor
(d) Variable capacitor is used in tuning circuits in ratio.
A. `a,b` only
B. `a,c` only
C. `a,b,c` only
D. `b,c,d` only
