The correct answer is: B. increase
In a closed-loop control system, the overall gain of the system is the product of the open-loop gain and the feedback gain. The open-loop gain is the gain of the system without feedback, and the feedback gain is the gain of the feedback loop.
The feedback loop is a circuit that compares the output of the system to the desired output, and then generates an error signal that is used to control the input to the system. The feedback gain is the gain of this circuit, and it determines how much the input to the system is changed in response to an error signal.
If the feedback gain is positive, then the feedback loop will tend to amplify any error signals. This means that the output of the system will be more sensitive to changes in the desired output, and the overall gain of the system will increase.
If the feedback gain is negative, then the feedback loop will tend to reduce any error signals. This means that the output of the system will be less sensitive to changes in the desired output, and the overall gain of the system will decrease.
In conclusion, the overall gain of a closed-loop control system will increase if the feedback gain is positive.