The potential gradient long the length of a unifrom wire is `10 "volt"//meter`. `B` and `C` are the two points at `30 cm` and `60 cm` point on a meter scale fitted along the wire. The potential diffenence between `B` and `C` will be
A. 3 V
B. 0.4 V
C. 7 V
D. 4 V
