二、单项填空(本节有10小题,每小题1分,共10分)21. Many people agree that ______ knowledge of English is a must in ______ international trade today.
__________, glasses can correct most sight defects in healthy eyes.
Is there anything ______?
If he __________, he would have passed the examination.
When we travel in other countries, we have to ________ lots of different customs.
Great changes ___ in the past ten years in China.