单项选择题
Since the burning or combustion takes place within the engine itself, the engine is known as （）.
A.a fire -tube boiler B.an internal combustion engine C.an external combustion engine D.an internal combustion generator
单项选择题 Shims of different thicknesses are inserted between the shells to enable adjustment of （）.
单项选择题 Sediment collects in a tubular purifier （）.
单项选择题 Sea water is not used directly as a coolant because of （）.
