Explanation:
When an ammeter is used in place of a voltmeter, it means we are trying to measure the voltage across a component using an ammeter. However, an ammeter is designed to measure current, not voltage. Therefore, in order to use an ammeter as a voltmeter, we need to modify its circuitry.

In order to measure voltage using an ammeter, we need to connect a high resistance in series with the ammeter. This is because voltage is directly proportional to current, and according to Ohm's Law (V = IR), if we increase the resistance (R), the current (I) will decrease. By connecting a high resistance in series with the ammeter, we limit the current flowing through the circuit and ensure that the ammeter does not draw too much current or damage the circuit.

Connection of high resistance in series:
Connecting a high resistance in series with the ammeter ensures that the current passing through the ammeter is limited, allowing it to measure the voltage drop across the component. The high resistance acts as a current limiter, preventing excessive current from flowing through the ammeter and the component being measured. This is necessary because an ammeter has a very low internal resistance, and connecting it directly across a component would result in a very low resistance path, causing a large current to flow and potentially damaging the ammeter and the circuit.

Why not low resistance in series:
If a low resistance were connected in series with the ammeter, it would not limit the current sufficiently, and the ammeter would still draw a large current. This would result in inaccurate voltage measurements and potential damage to the ammeter and the circuit.

Why not low resistance in parallel:
Connecting a low resistance in parallel with the ammeter would result in a short circuit. This would bypass the component being measured and cause the majority of the current to flow through the parallel low resistance path. The ammeter would not be able to accurately measure the voltage drop across the component, and the current flowing through the ammeter would be much higher than intended, potentially damaging the ammeter and the circuit.

Therefore, connecting a high resistance in series with the ammeter is the correct choice when using an ammeter as a voltmeter.