The correct answer is: A. Zero.
A voltmeter is an instrument used to measure the voltage (electrical potential difference) between two points in an electric circuit. It is a type of ammeter, an instrument used to measure electric current.
A voltmeter should have zero resistance so that it does not affect the circuit it is measuring. If the voltmeter had any resistance, it would introduce a voltage drop in the circuit, which would affect the measurement.
Option B is incorrect because a voltmeter with very high resistance would not be able to measure the voltage accurately. The voltage drop across the voltmeter would be too small to be measured.
Option C is incorrect because a voltmeter with very low resistance would draw too much current from the circuit. This could damage the voltmeter or the circuit.
Option D is incorrect because it does not provide a correct answer.