有()的采掘工作面,必须有专人经常检查,并安设甲烷断电仪
A.突水危脸
B.煤与瓦斯突出危险
C.瓦斯喷出危险
D.瓦斯涌出大、变化异常
参考答案:B, C, D
下列说法错误的是( )
A.6.02×1023是阿伏加德罗常数的近似值
B.1mol 12C的质量是12g
C.含有阿伏加德罗常数个粒子的物质就是1mol
D.1mol O2含有6.02×1023个氧原子
Stephen Hawking believes that the earth is unlikely to be the only planet _______ life has developed gradually.
A.that
B.where
C.which
D.whose