Introduction:
The increase in operation speed of a computer system can be achieved through various techniques. One of these techniques involves reducing the reference voltage. This answer will explain why reducing the reference voltage can lead to an increase in operation speed.

Explanation:
Reducing the reference voltage is a technique used to improve the performance of digital circuits. It is commonly known as voltage scaling or supply voltage scaling. By lowering the reference voltage, the power consumption of the circuit is reduced, which in turn allows for higher clock frequencies and faster operation speed. Below are the reasons why reducing the reference voltage can increase the operation speed:

1. Power Consumption:
When the reference voltage is reduced, the power consumption of the circuit decreases. This is because the power consumed by a digital circuit is directly proportional to the square of the supply voltage. By lowering the reference voltage, the power dissipation is reduced, leading to lower energy consumption.

2. Heat Dissipation:
Reducing the reference voltage also helps in reducing the amount of heat generated by the circuit. Heat dissipation becomes a critical factor as the clock frequency increases. By reducing the reference voltage, the circuit generates less heat, which allows for higher clock frequencies to be achieved without overheating the system.

3. Timing Constraints:
Timing constraints are an important aspect of digital circuits. When the reference voltage is reduced, the timing constraints can be relaxed. This means that the circuit can operate at higher clock frequencies without violating the timing requirements. This leads to an increase in operation speed.

4. Signal Integrity:
Signal integrity refers to the quality of the electrical signals within a circuit. When the reference voltage is reduced, it helps in improving the signal integrity. This is because reducing the reference voltage reduces the noise margin, which in turn reduces the likelihood of signal degradation. Improved signal integrity allows for faster and more reliable operation.

Conclusion:
Reducing the reference voltage is a technique used to increase the operation speed of a computer system. By reducing the reference voltage, the power consumption, heat dissipation, and timing constraints of the circuit are improved. This allows for higher clock frequencies and faster operation speed. Therefore, the correct answer to the question is option 'A' - reducing the reference voltage.