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 will 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………………………………………………………….