be behind in doing sth

be behind in doing be behind in doing sth fall behind in 和be behind in 的区别~ be occupied in doing be expert at doing 还是in doing be in charge of doing be interested in doing sth be busy in doing sth be long in doing sth be sophisticated in doing sth be absorbed in 后可以加doing sth.还有focus one's attention on ,on后面可以加doing sth. be busy doing 和 be busy in doing 的区别? be successful in doing in可省吗 英语标序号( )Oh!I see him.He's behind the tree.( )He'sdrawing quietly.( )Where is Jim?( )What's he doing?( )No,he is not in the car.( )I don't know.Is he in the car? I am be way behind in my letter writting 还有这里的way 和be behind in 的意思 be worth doing sth .doing前面加in么? be interested in为什么加doing [急]be interested in后是加doing么?