纤维状粉尘一般是指纵横径之比()
A.<2:1的粉尘
B.>2:1的粉尘
C.>3:1的粉尘
D.>5:1的粉尘
E.>10:1的粉尘
参考答案:C
Having entered the classroom, the teacher ___ the book on the desk.
A.laid
B.lied
C.lay
D.lain
矿井五大自然灾害指水、火、瓦斯、煤尘、()。
A.电气事故
B.机械事故
C.顶板事故