The team are working hard to ___ the problem so that they can find the best solution.
He looked quite healthy ____ he was ____ the age of seventy.
Does John know any other foreign languages ____ French?
The old man died ____ cold ____ a cold night.
The trees ____ front of the house are ____ the charge of Old Li.
- Do you go there ____ bus? - No, we go there ____ a train.