The correct answer is: A. Manipulated variable
The manipulated variable is the input to a control system that is used to control the output of the system. It is the variable that is changed by the controller in order to achieve the desired output.
The reference input is the desired value of the output of the control system. It is the value that the controller tries to achieve by changing the manipulated variable.
The primary feedback is the measurement of the output of the control system. It is the signal that is used by the controller to determine how much to change the manipulated variable in order to achieve the desired output.
The zero sequence is a component of a signal that is not affected by changes in the frequency of the signal. It is the component of a signal that is constant over time.
The actuating signal is the signal that is sent to the final control element in order to control the output of the control system. It is the signal that is the result of the controller’s decision making process.
In conclusion, the manipulated variable is the input to a control system that is used to control the output of the system. It is the variable that is changed by the controller in order to achieve the desired output.