1/ If they understood the problem, they would find a solution.
 2/You will be late for the train if you don't go right now.
 3/They would understand you if you didn't speak English unnaturally
 4/If we had known your phone number, we could have contacted yo. 
 5/ If Simon lived near his mother, he could visit her often. 
 6/If she had hurried, she wouldn't have missed the train. 
 7/ If John didn't eat many chips, he wouldn't be fat. 
8/ Unless you tell Bill what to do, he never does anything.