可燃气体或蒸气与空气的混合物，若其浓度在爆炸下限以下或爆炸上限以上时便不会着火或爆炸。
参考答案：错
、To our great surprise, the disabled person made a requirement that he as a volunteer
A．received
B．was received
C．be received
D．would receive
以下不是功率单位的是（）
A、马力
B、瓦特
C、千瓦
D、卡
