单项选择题
A.instigating corrective action B.indicating values of controlled variables C.warning of off-limit conditions D.providing record of performance
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
A.the lack of a feedback B.the presence of a feed back C.the lack of a computer D.the presence of a computer