列车司机在列车运行中，遇有信号显示不明或危及行车和人身安全时，应立即采取（）措施。
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If you have to jump in the water when abandoning a vessel，your legs should be（）.
A. spread apart as far as possible
B. held as tightly against your chest as possible
C. in a kneeling position
D. extended straight down and crossed at the ankle
试分析用平旋盘刀架镗孔及用主轴镗孔时，同轴度超差的原因。
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