I think she is right but I am not completely sure.
This is a common mistake ____ students.
If you run ____ two hares you will catch neither.
His grandfather died ____ the wound that the enemy soldier had given him .and then his grand- mother died ____ hungry and cold.
The teacher is not only strict ____ his pupils but also strict ____ his own work.
Mary dropped in ____ Mr Smith, but he wasn' t at home, so she went to drop in ____ Mr Smith's office.