A wire of length L and resistance R has uniform cross section. A potential difference of 10 volt is applied across the wire as shown. A cell of emf E (< 10 volt) and of internal resistance r is connected through a galvanometer between points A and C. The point C, at a distance I from A, is chosen such that the galvanometer reads zero. The length I depends on
(A) E only
(B) E and L only
(C) E and r only
(D) E, r and L only