1、Beijing expects China's rich civilizations to ____ the world with a happy surprise at the opening ceremony of the 2008 Olympic Games.
A.showB.attractC.presentD.perform
(答案是C。为什么A不可以呢？)
2、I've got spots on my face,I ____ take more vitamin A.
A.willB.mustC.canD.have to
(答案是D。A和B为什么不可以？)
3、-Can I pay the bill next month?
-Sorry,sir.But it's the rule of our company that all payments ____ be made by the end of the month.
A.canB.needC.willD.shall
（答案是D。为什么B不可以？）
4、It ____ seven days since she ____ down the stairs,but you can still see the bruise.
A.was;fellB.is;has fallenC.is;fellD.will be;fell
（A和B各应该在什么情况下用啊？）
