State the uses of a potentiometer. Why is a potentiometer preferred over a voltmeter for measuring e.m.f.?

a) Potentiometer measures current; voltmeter measures potential difference
b) Potentiometer measures potential difference; voltmeter measures current
c) Potentiometer is more accurate; potentiometer does not draw current from the circuit
d) Voltmeter is more accurate; voltmeter does not draw current from the circuit