Introduction:
An operational amplifier (op-amp) comparator is an electronic device that compares two input voltages and provides an output based on the voltage difference between them. The speed of operation of an op-amp comparator is an important consideration in many applications. In order to achieve higher speed of operation, it is necessary to choose an op-amp comparator with a wider bandwidth.

Explanation:
Bandwidth:
The bandwidth of an op-amp comparator refers to the range of frequencies over which the device can operate effectively. It determines the maximum frequency at which the comparator can respond to changes in the input voltages. A wider bandwidth allows the op-amp comparator to respond to high-frequency signals more quickly, resulting in a higher speed of operation.

Gain:
The gain of an op-amp comparator determines the amplification of the input signal. While a large gain can provide better accuracy in certain applications, it does not directly affect the speed of operation. Therefore, choosing an op-amp comparator with a large gain does not necessarily result in a higher speed of operation.

Slew Rate:
The slew rate of an op-amp comparator refers to the maximum rate of change of the output voltage. It indicates how quickly the output voltage can change in response to a change in the input voltages. While a high slew rate is important for accurately reproducing fast-changing signals, it does not directly affect the speed of operation. Therefore, choosing an op-amp comparator with a high slew rate does not necessarily result in a higher speed of operation.

Conclusion:
In conclusion, the correct answer is option 'C' - choosing an op-amp comparator with a wider bandwidth. A wider bandwidth allows the op-amp comparator to respond to high-frequency signals more quickly, resulting in a higher speed of operation. While a large gain and high slew rate are important considerations in certain applications, they do not directly affect the speed of operation of an op-amp comparator.