1. There is sth wrong with my knee.
=(Something is wrong) with my knee.
2. I've got a sharp pain in my left leg.
=My left leg (hurts badly).
3. The doctor advise that she should not have greasy food.
=The doctor advise (her not to) have greasy food.
4. While crossing the street,we should watch out for cars.
=While crossing the street,we (had better be careful) with cars.