单项选择题
Which pump is the self-priming pump?（）
A.turbine B.centrifugal C.ejector D.mixed flow
单项选择题 The younger motorman as well as the others （） to operate the oil separator.
单项选择题 A water pump can not supply water after startingIt may be caused by （）.
单项选择题 Dress up the （）.
