For comparing the e.m.f.'s of two cells with a potentiometer, a standard cell is used to develop a potential gradient along the wires. Which of the following possibilities would make the experiment unsuccessful [MP PMT 1994]

• A.                    The e.m.f. of the standard cell is larger than the E e.m.f.'s of the two cells
• B.                    The diameter of the wires is the same and uniform throughout
• C.                    The number of wires is ten
• D.                    The e.m.f. of the standard cell is smaller than the e.m.f.'s of the two cells