In open loop system

the control action depends on the size of the system
the control action depends on system variables
the control action depends on the input signal
the control action is independent of the output

The correct answer is: D. the control action is independent of the output.

In an open-loop system, the control action is not affected by the output of the system. This means that the control action is determined solely by the input signal and the system’s characteristics.

Option A is incorrect because the control action does not depend on the size of the system.

Option B is incorrect because the control action does not depend on system variables.

Option C is incorrect because the control action does not depend on the input signal.