矿井总回风流中CH4的浓度不得超过（）%。
A.0.5
B.0.75
C.1
参考答案：B
It's ___________ orange. It's ___________ orange orange.[ ]
A. a, an
B. an, an
下列杂交组合属于测交的是[ ]
A．EeFf×EeFf
B．ffgg×FfGg
C．ffGg×FfGg
D．EeFf×eeFf
