A( is a device used to ensure positive position of a valve or damper actuator a. calibrator b. positioner c. actuator d. characteristic cam

C) actuator

Explanation:

Actuator is the device that used to provides the power and manipulate the motion of the moving parts of the valve and damper is used to control the flow of the fluid. Actuator is the device or the mechanism which are used to control valve automatically and valve is a device which is used to control and regulate the fluid by rotating the flow.