（）表明油品在低温条件下的流动性，对油品的输送和使用具有很大的重要性。
A、闪点
B、燃点
C、自燃点
D、凝点
参考答案：D
A hydrostatic release mechanism for a liferaft（）.
A.must be wet before it will release
B.should be kept in a watertight except in an emergency
C.will inflate the raft in its cradle if operaterd manually
D.must be submerged to a certain depth to release automatically
乙炔既是可燃性气体，又是易（）气体。
