单项选择题
A.adjusting a nut B.a pre-tensioned spring C.any spring D.upstream pressure
Most marine biological sewage treatment plants consist ...
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
To prevent accidents from occurring, special valve ches...
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
A check valve is another name for （）.A.a test valveB.an...
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
