What Is a process variable? A. A manipulated variable B. A controlled variable C. A process parameter that changes value D. All of the above E. None of the above

The correct answer is: C. A process parameter that changes value.

A process variable is a parameter of a process that changes value. It is usually measured and controlled to ensure that the process is operating within its desired operating range.

A manipulated variable is a variable that is changed in order to control another variable. For example, the flow rate of a fluid may be the manipulated variable in order to control the temperature of a process.

A controlled variable is a variable that is maintained at a desired value by adjusting the manipulated variable. For example, the temperature of a process may be the controlled variable.

Therefore, the correct answer is C. A process parameter that changes value.