单项选择题

Most marine biological sewage treatment plants consist of all the following statements except （）.

A.aeration tanks
B.settling tanks
C.disinfection agent
D.anaerobic bacteria

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单项选择题

To prevent accidents from occurring, special valve chests are used in such cases in which interchangeable blanks and connecting passages are incorporatedThe bold and italic word “which” means （）.

A.accidents
B.special valve chests
C.interchangeable blanks
D.connecting passages

单项选择题

A check valve is another name for （）.

A.a test valve
B.an inspection valve
C.a stop valve
D.a non-return valve

单项选择题

A butterfly valve consists basically of a disc pivoted across the bore of a ring body having the same radial dimensions as the pipe in which it is fitted.According to the above sentence, which of the following statements is not true?（）

A.The diameter of a disc is the same as the outer diameter of the pipe
B.We can infer that the valve is opened or closed by rotating the spindle
C.A butterfly valve comprises a disc and a ring body
D.The profile of the butterfly valve is a ring body