初中英语的几个句子问题
This is so difficult a problem that few of us can work it out.(为什么要有a,可不可以so difficult a换成such)
Fran,with his two sisters,is leaving for London by train which leaves at 8:00 next morning,（为什么用这样的时态）
Great changes have taken piace in our province.Many tall buildings have been set up.(为什么是这样的时态）
Roller-skating is a sport that people of all ages can enjoy.(为什么用that,不可以what)
Sam is my best friend whose father is very tall.(为什么是whose,
最后再给我说说,做这种题的技巧.还有,一些句子中,什么时候用do,什么时候用is,我到现在还有时候会搞混……