What is the purpose of the landing gear transfer unit?

What is the purpose of the landing gear transfer unit?

A.A.If hydraulic B fluid is lost the landing gear can be extended by automatic activation of the transfer unit

B.B. In case of No1 engine failure/separation, the gear can be retracted after takeoff.

C.C.In case of engine failure the gear can be retracted in order to reduce drag for the cruise segment.

D.D.If hydraulic A fluid is lost, the transfer unit must be manually selected to B fluid when the gear lever is selected up.

正确答案是B