The delivery rate of an axial-piston hydraulic pump is controlled by varying the position of the （）.

A.overfeeding of the expansion valve
B.damage to the condenser
C.constant running of the compressor
D.flooding of the receiver

A.horsepower
B.work
C.heat
D.velocity

A.compressor lubrication will be improved
B.oil will not leave the crankcase
C.compressor valves will be damaged
D.oil may congeal in the evaporator