单项选择题
A.central air conditioning system
B.high velocity system
C.low velocity system
D.single duct system
单项选择题 The（） only allows for adjustment of temperature in each room by the occupant manually controlling the air volume admitted.
单项选择题 The volute of centrifugal pump also acts as a diffuser converting （）into pressure head.
单项选择题 A centrifugal impeller consists of a number of vanes curving （） from the direction of rotation.