单项选择题
A.more efficiently uses available engine power
B.operates at a lower efficiency at a fixed speed
C.produces the same torque at lower engine power
D.develops its rated power at a lower speed
单项选择题 Compared to a constant pitch propeller, a controllable pitch propeller（）.
单项选择题 Which of the following statements describes the functions of a reservoir used in a hydraulic system?（）
单项选择题 Which of the following statements describes the functions of a reservoir used in a hydraulic system?（）