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1. If it weren't too cold, they could go swimming.

2. If we had known you were in hospital, we would have visited you.

3. If the doctors could find out the remedy, they could save a lot of people.

4. If we used public bus service, we would get rid of pollution in the city.

Câu đk loại 2 (không có thật ở hiện tại): If S V2/ed, S would/could V

Câu đk loại 3 (không có thật ở quá khứ): If S had V3/ed, S would/could have V3/ed

1 if it weren't too cold , they could go swimming

2 if we had known you had beeb in hospital , we would have visit you

3 if the doctors found out the remedy , they could save a ot of people

4 if we used public bus service , we would get rid of pollution in the city