1.he doesn't take any exerciese .he is so unhealthy.

=>if......he took exerciese .he would be healthy.......

2.study hard or you won't pass the exam.

=>if...you study hard, you won't pass the exam.......

3.don't be impatient or you will make mistakes.

=>if.......you don't be impatient ,you will make mistakes........

4.i didn't eat lunch, i feel hungry now

=>if i.......had eaten lunch,I wouldn't feel hungry now.......

5.if you wanted my advice,i wouldn't buy it

=>if i.........were you,i wouldn't buy it.......

6.i only come if they invite me

=>unless.......they invite me,i won't come.........

7.he didn't revise all his lessons, he failed the exam

=>if he..he had revised all his lessons, he wouldn't have failed the exam....

8.leave me alone or i'll call the police

=>unless.....you don't leave me alone ,i'll call the police.......