11. Because his leg was broken, Harry had to stay in the hospital
12. Jim had to give up jogging because he had sprained his ankle severly.

=> Jim had to give up jogging because of his severe sprained ankle.

13. The water in most rivers is unsafe to drink because it's polluted.

=> The water in most rivers is unsafe to drink because of being polluted.

14. We had to stay in London an extra day because it was foggy at the airport.

=> We had to stay in London an extra day because of the foggy at the airport.
15. John has to sit in the front row in class because he has poor eyesight.

=> John has to sit in the front row in class because of having poor eyesight.