单项选择题
A.a closed loop control system
B.an open loop control system
C.a boiler control system
D.a steering gear control system
单项选择题 This arrangement is （） if the elements are directly connected to one another and the control action takes place without human involvement.
单项选择题 Bourdon Tube is probably the most commonly used （） measuring instrument.
单项选择题 Movement of the diaphragm or bellows is （） by a linkage to a needle or pointer display to indicate the differential pressure between two sides of the diaphragm or bellows.