In order not to be disturbed ,I spent three days ________ in my study.  

Many parents happily pay a lot of money, only ______ the tours are not rewarding enough for their children.

When I entered the classroom, I saw Mary ______ at the desk and ______ a letter.

--Do you have any trouble _____the work? ---No． in fact we have finished it already．

Every minute is made full _________ of ________ our lessons well.