这些操纵面是液压作动的，并且在起飞和降落时展开或收回。( )
A.These control surfaces are hydraulically supplied and are only extended or retracted during take off and landing. B.These control surfaces are hydraulically moved and are only extended or retracted during takeoff and landing. C.These control surfaces are hydraulically powered and are only extended or retracted during takeoff and landing.正确答案C
