题目内容：

—How should we deal with air pollution?—It will be very difficult _____ there are fewer factories and cars.[ ]
A.until B.unless C.if D.after
为什么是选B?A为什么不可以?理解为直到车和工厂少了之后解决空气污染就不会困难了不可以吗?

优质解答

B肯定正确,下面只说A用A的话,要改成：It will have been very difficult until there are fewer factories and cars. 直到工厂和车子都少了以后,解决空气污染都会一直困难.这样改只是在语法上行得通,一般不这样用,因...