He didn't want to see anybody, so he spent six hours ________ in the small room.

Mr. Smith is busy these days ________ a new book on how to develop a child’s reading skill.

he problem will be fully discussed at the meeting ______the next day.

 Unless ________ to answer questions, the pupils won't talk in Mrs Smith's class.

Dr Yuan makes______ possible______ one-third more of the crop in the same fields.