1. If we had taken the train, we wouldn't have been late for the meeting.

-> If 3: If + S1 + had + Vpp, S2 + would have + Vpp

2. The meat was so rotten that I had to be thrown away.

-> S + be + so + adj + that + S + V

3. You don't have to finish by Saturday.

-> neccessary = have to = need 

4. The youth was made to empty his pocket by the police.

-> Bị động với "make" S + be + made + to V 

5. It takes six-hour to drive from London to Edinburgh.

-> It + takes + SO + thời gian + to V

1.if we had taken the train,we wouldn't have been late for the meeting-câu đk 3 diễn tả hành động,sự việc ko có thật ở quá khứ

2.the meet was so rotten that i had to be thrown away-S + V + so + adjective/ adverb + that + S + V 

3.you don't have to finish it by Saturday-don't have to=it is not necessary

4.the youngth was made empty his pocket by the police-chủ ngữ câu này là tân ngữ câu kia->bị động

5.it takes six hours to drive from London to Edinburgh-it takes/took(sb)+time+toV