某气体在近地面空气中浓度稍大时是一种污染物，而在高空中却对人类有保护作用，该气体是（）.
A.NO
B.O3
C.CO
D.氯氟烃
参考答案：B
Alien had to call a taxi because the box was _____ to carry all the way home．
A．much too heavy
B．too much heavy
C．heavy too much
D．too heavy much
在常温下，液化石油气液体单位体积的重量比水（）
A、重
B、轻
C、差不多
D、不好比
