We have a big library ______ lots of useful books.

Simon is willing to help others _________ with their English.

Do you know the answer _______ the question.
A. to         B. of          C. at        D, in

Thanks ________ the photo of your family.
　　    

The baseball is on the floor, ________ the bookcase and the desk.

Tim, thank you_______ your eraser.

Please call me ______ 235—5680.

Don’t play tricks ______ that little child, he is crying.

We knock _____people’s doors, and they usually give us some candy _____ a treat.
A. on, to           B, at, to           C. on, as           D. on, on

Sorry, I don’t know the answer _______ the question_______ it is too hard.