The correct answer is D. all of the above.
Static error coefficients are used as a measure of the effectiveness of closed loop systems for specified input signals. They are used to determine how well a system will track a desired input signal. The static error coefficient for a given input signal is the steady-state error that results when the system is in steady state and the input signal is applied.
The static error coefficient for position is the steady-state error that results when the system is in steady state and a step input is applied. The static error coefficient for velocity is the steady-state error that results when the system is in steady state and a ramp input is applied. The static error coefficient for acceleration is the steady-state error that results when the system is in steady state and a parabolic input is applied.
Static error coefficients are important because they can be used to design closed loop systems that will track desired input signals with a minimum amount of error.