Introduction:
Loading effect refers to the alteration of the measured quantity due to the presence of the measuring instrument in the circuit. In the case of a voltmeter, the loading effect occurs when the internal resistance of the voltmeter circuit affects the voltage being measured. To avoid or minimize this loading effect, certain measures can be taken.

Explanation:
The correct answer to avoid the loading effect in a voltmeter is option 'C', i.e., using a high sensitive voltmeter. Here's an explanation of why this is the correct choice:

1. Understanding the Loading Effect:
When a voltmeter is connected in parallel to a circuit, it acts as a load and draws some current from the circuit. This current flows through the internal resistance of the voltmeter, causing a voltage drop. As a result, the voltage being measured by the voltmeter is slightly lower than the actual voltage in the circuit.

2. Importance of Sensitivity:
The sensitivity of a voltmeter is a measure of its ability to detect and display small changes in voltage. A high sensitive voltmeter can measure small voltages accurately without significantly affecting the circuit being measured. On the other hand, a low sensitive voltmeter may draw more current from the circuit, resulting in a larger loading effect.

3. Effect of Sensitivity on Internal Resistance:
A high sensitive voltmeter typically has a very high input impedance or internal resistance. The input impedance of a voltmeter is the resistance that it presents to the circuit being measured. A higher input impedance means that the voltmeter draws less current from the circuit, minimizing the loading effect.

4. Alternate Options:
The other options provided in the question, such as using a high voltage range or an accurate and precise instrument, do not directly address the loading effect issue. While using a high voltage range may prevent the voltmeter from saturating, it does not necessarily minimize the loading effect. Similarly, an accurate and precise instrument ensures accurate measurements but does not directly address the loading effect.

Conclusion:
To avoid or minimize the loading effect in a voltmeter, it is important to use a high sensitive voltmeter with a high input impedance. This ensures that the voltmeter draws minimal current from the circuit being measured, resulting in more accurate voltage measurements.