单项选择题
A.globe valves B.butterfly valves C.gate valves D.reducing valves
A number of biological sewage treatment plants are in u...
单项选择题A number of biological sewage treatment plants are in use at sea but nearly all work on what is called the extended aeration processBasically the consists of oxygenating the liquor by bubbling air through itAccording to the above two sentences, the word "this" means （）.
A.a sewage treatment plant B.the extended aeration process C.the liquor D.the bubbling air
Explosions do occur （） caused by the ignition of oil or...
单项选择题Explosions do occur （） caused by the ignition of oil or vapour gaining access from compressors or defective engine starting valves.
A.in boiler drums B.in refrigerating plants C.in starting air pipes D.in air coolers
Air reservoirs are designed, built and tested similarly...
单项选择题Air reservoirs are designed, built and tested similarly to （）.
A.boiler drums B.hot wells C.condensers D.evaporators
