6-Don’t stay up late or you’ll be tired tomorrow.      
 -> If you.....stay up late, you'll be tired tomorrow.................................................
7-Don’t be lazy or you ‘ll  fail the exam.     
-> If you......are lazy, you'll fail the exam................................................................
8-I am not rich ,so I can’t buy a house .      
 -> If I were....rich, I could buy a house...............................................................
9-This car is expensive, so we can’t buy it.        
->If this car........weren't expensive, we could buy it..................................................
10-He doesn’t get high scores because he is lazy.   
 ->If he........weren't lazy, he would get high scores.....................................................
11-Money doesn’t grow on trees,we aren’t rich.       
-> If  money .......grew on trees, we would be rich..........................................
12-He  is too short to play  basket ball.       
-> If he................were tall, he could play basketball........................................................
13-We can’t go on a picnic because the weather is not fine.   
-> If the weather......were fine, we could go on a picnic...........................
14-If I don’t live in a big city,I can’t go to the supermarket very often.    
-> Unless......I live in a big city, I can't go to the supermarket very often..................
15-I can’t buy a computer if I don’t have money.   ->Unless...I have money, I can't buy a computer.....................................................
16.You can get high marks if you are not lazy.
->Unless ………………you are lazy, you can get high marks…………………………………………….
17.We ‘ll go camping if the weather is not good.
->Unless………the weather is good, we 'll go camping………………………………………………………..
18.If she is lazy,she will not pass the exam.
->Unless………she is lazy, she will pass the exam……………………………….
19.If Nam doesn’t speak English everyday, he will easily forget how to use it. 
=> Unless ……Nam speaks English everyday, he will easily forget how to use it………………………………………………………