3. if... ... +
If I were you, I would accept his offer.
If the government worked more efficiently, more people would vote.
What would you do if you were bitten by a cobra.
What would Japan do if the OPEC countries cut their oil supply.
4. if... ... +
If I had had enough money, I could have bought the picture
What had happened if I had not smelled gas?
If I had voted against him, he would have had to resign
If I had been sensible, I should have known I had no chance.
6. • if... ... will[shall]+
If need be, you can use my car.
I can come and help you with your work if need be
If any person be found guilty, he shall have the right of appeal
If it be inappropriate to have said this, I humbly apologize.