On what type of pump would you find an impeller?（）

A.A flashing light combined with a fixed light of greater brightness
B.Light flashes combined in groups，with a different number of flashes in each group
C.A light showing groups of two or more flashes at regular intervals
D.A fixed light varied at regular intervals by groups of two or more flashes of greater brightness

A.auxiliary guys
B.extra fair leads
C.steel bands
D.stops

A.be open to view so，if a foreign object gets in the gearing，the operator can immediately stop the machinery
B.have a guard over the gearing
C.be painted a contrasting color from the base color in order to call attention to the gearing
D.not be operated if there is any crew within 10 feet of the machinery