26 I can't write to Linh because I don't have her  address

-> if i had linh's address, i could write to Linh
27 Dick often causes accidents because he drives carelessly

-> if dick didn't drives carelessly, he wouldn't cause accidents
28 we can't give much help to the poor because we waste a lot of money on unnecessary things
->If we didn't waste a lot of money____, we couldn't___
29. Peter is fat because he eats so many chips.
->If Peter didn't eat so many chips,he would not be fat
30   Be calm, or you’ll make a wrong decision.
->If you are calm, you won't make a wrong decision.