单项选择题
A water pump can not supply water after startingIt may be caused by （）.
A.closed discharge valve B.broken pipe line C.worn shaft D.both A and B
单项选择题 Dress up the （）.
单项选择题 A mixed-flow pump is a （） pump classified by the working principle.
单项选择题 The （）pump is usually used as the bilge feed pump to an oily water separator.
