The teacher told us that the problem was not _____ easy and that we should think _____ over carefully.
Everyone in the village is very friendly. It doesn't matter ____ you have lived there for a short or a long time.
(2012江西卷)It suddenly occurred to him he had left his keys in the office.
As many five courses are provided, and you are free to choose ______ suits you best.
Scientists study ____ human brains work to make computers.
(2012辽宁卷)The newcomer went to the library the other day and scarched for he could find about Mark Twain.