单项选择题

The internal part of boiler should be welded by yard if found （）.

A.sealed
B.cracked
C.shape changed
D.deformed

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单项选择题

A.deformed
B.rusted
C.cracked
D.scaled

单项选择题

A.in series
B.in parallel
C.either A or B
D.None of the above is tree

单项选择题

Which of the following pumps are self-priming, and can deal with liquid from a level below the pump: （）
(1)reciprocating
(2)vane
(3)gear

A.（1）only
B.（1）and（2）
C.（2）and（3）
D.（1），（2）and（3）