The current through any `p-n` junction is due to
(a) drift of charge carriers
(b) diffusion of charge carriers
( c) different concentrations of same type of charge carriers in different regions.
(d) Same concentrations of same type of charge carriers in different regions
A. `a,b` and `c`
B. `a` and `b` only
C. only `d`
D. `a,b,c,d`