What is the control law equation for speed regulation in a proportional control system?

A) u=K(vr-v)
B) u=K(vr-v) where vr is the reference speed and K is a constant
C) u=K(vr-v) where vr is the reference speed and K is a constant. This is a proportional control law that uses the difference between the reference speed and the actual speed as a signal to adjust the engine speed.
D) u=K(vr-v) where vr is the reference speed and K is a constant. This is a proportional control law that uses the difference between the reference speed and the actual speed as a signal to regulate the engine speed.