题目内容
（请给出正确答案）
[主观题]
Diesel engine ‘blow-by’ into the crankcase is caused by excessive ring______.
A.back clearance
B.side clearance
C.gap clearance
D.taper clearance
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A.a separate air ejector unit
B.a direct unimpeded connection between second stage and salt water feed heater
C.either by vacuum drag or an external line from the first stage via a fixed orifice
D.the fixed orifice provided in the steam supply line
