Consider a current carrying wire in the shape of a circle. Note that as the current progresses along the wire, the direction of j (current density) changes in an exact manner, while the current I remain unaffected. The agent that is essentially responsible for is:

Options

A. (a) source of e.m.f.
B. (b) electric field produced by charges accumulated on the surface of wire.
C. (c) the charges just behind a given segment of wire which push them just the right way be repulsion?
D. (d) the charges ahead