— Some Chinese students find it hard to get used to the life in London.  

— Exactly, ______ they've learnt a lot about the city before. [ ]

A. if

B. now that

C. as though

D. even though

采用可重入程序是通过使用______的方法来改善响应时间的。

A．减少用户数目

B．改变时间片长短

C．加快对换速度

D．减少对换信息量