单项选择题
A.avoid false alarms as a result of condensing water vapor
B.avoid danger of frost under very cold weather
C.reduce the viscosity of the crankcase atmosphere in order to improve the fluidity
D.keep the temperature of the oil mist detectors in an appropriate range
单项选择题 （）continuously extract the crankcase atmosphere, via a pipe system, and move it past a sensitive and accurate opacity measuring track.
单项选择题 The oil mist detectors continuously（） the crankcase atmosphere, via a pipe system, and move it past a sensitive and accurate opacity measuring track.
单项选择题 （）, the repair in so short a time is unknown to us.