mình làm rồi mong các bạn sửa giùm

he wasn't feeling well , so he didn't do well in the exam

if he was feeling well, he would do well in the exam

2 Tom speaks English very well
tom has studied English for a long time.
3 I haven't written to him for a long time

it is a long time since the last time I wrote to him.

4 I'll see you next week unless something unexpected happens

if something unexpected doesn't happen, I 'll see you next week.

5 this is the biggest fish I have ever seen
never before I have seen a fish bigger than this.

6 i'm sorry i can't understand anything
I wish I could understand something