It was wrong to cut down the old tree which dates back to 1915, _______ the reason．

This hotel is the highest building in the city, from ______ top you can enjoy a good view of our city.

________ hard one may work, one cannot master a foreign language in a month or two. 

After Yang Liwei succeeded in circling the earth ,_______our astronauts desire to do is walk in space .

Choosing the right dictionary depends on ______ you want to use it for.