此题就是选B。从后面的主语could not walk来判断,这是个虚拟语气的句子。当if引导的非真实条件句中含有were, should, had时可以把if 省略,把were ,had ,should 提前。所以这句话正常语序是 if there were no friction(如果没有摩擦的话)又如:Should it rain tomorrow, we would not go outing.Had he followed my advice, he would have passed the exam.加油!!...
这道题考的是therebe 的用法,一般be用单数还是复数由他后面所接的词的单复数决定。即be的数与后面的名词一致,若be后是两个或多个并列的名词,be则与靠得最近的那个名词的数一致。 friction是不可数名词,因此选B。期中between the surface of the road and our feet做定语修饰friction,对其做解释...