一Be careful , you will make mistakes in your exams. —I know that,Mum. One can never be too careful.
Mr. Smith lives ____ that building. His house is ____ thefifth floor.
We will never forget what happened ____ the afternoon of May12, 2008.
It’s very kind ____ them to pick me up at the railway stationand drive me home.
–What do you often do ____ classes to relax yourself?–Listen to music.
We looked at each other ____ surprise when we heard a bird singing “Happy birthday to you”.