易燃介质是指与空气混合的爆炸下限小于10％或爆炸上限和下限之差小于等于20％的气体。
参考答案：错
A “full service” Loran-C receiver will provide（）.
A.matching pulse rates of at least 20 stations
B.an automatic on-and-off switch
C.a horizontal matching of all delayed hyperbolic signals
D.automatic signal acquisition and cycle matching
如何评价氧疗的效果？
