单项选择题
A feedback is an input（）
A.which governs the state of a variable B.which provides a visual and audible alarm C.which indicates values of controlled variables D.which measures the state of the controlled variable
单项选择题 The closed-loop system differs from the open-loop system by（）
单项选择题 From the passage, we can learn that the simplest controller action is（）
单项选择题 Which kind of the following controllers is the most sophisticated controller?（）
