The correct answer is A) input impedance much greater than the impedance across which the voltage is being measured. When troubleshooting electronic circuits, using a voltmeter with a high input impedance helps minimize the 'loading effect' on the circuit. The high input impedance of the voltmeter ensures that it draws very little current from the circuit, reducing the impact on the voltage being measured. This preserves the original voltage conditions in the circuit, providing a more accurate reading. The other options are incorrect because: B) A sensitivity of more than 1000 volts/ohm does not address the loading effect. C) An input impedance much less than the circuit impedance would significantly load the circuit, causing an inaccurate voltage reading. D) A sensitivity of less than 1000 ohms/volt does not relate to minimizing the loading effect.