A potentiometer is preferred over a voltmeter to measure the emf of a cell because…
(A) The material of the potentiometer wire has a low temperature coefficient of resistance.
(B) emf measured by potentiometer is more accurate because the cell is open-circuit.
(C) potential gradients can be varied in a potentiometer using a rheostat.
(D) Potentiometer is more sensitive than voltmeter.