Sử dụng câu điều kiện để viết lại các câu sau

Sử dụng câu điều kiện để viết lại các câu sau 
17.But it hadn’t been for his help, you couldn’t have done anything.

=>If

18.If there hadn’t been thick fog, our flight wouldn’t have been delayed.

=>Without

19.If they hadn’t given us useful advice, we wouldn’t have been able to get out of such trouble.

=>Without

20.Without her prevention, we could have been in trouble.

=>If