单项选择题
The tube in a boiler should be blinded if found （）.
A.scaled B.informed C.leaky D.deformed
单项选择题 The internal part of boiler should be welded by yard if found （）.
单项选择题 The internal part of the boiler, if found （）, has to be chemically washed by yard.
单项选择题 Centrifugal pumps can be designed with a number of impellers （） to attain a high final delivery pressure.
