Compared to a constant pitch propeller, a controllable pitch propeller（）.

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

A.Dissipate heat
B.Trap foreign matter
C.Separate air from the oil
D.All of the above

A.Dissipate heat
B.Trap foreign matter
C.Separate air from the oil
D.All of the above