到 http://cache.baidu.com/c?word=%D6%D8%D7%B0%3B%B2%D9%D7%F7%3B%CF%B5%CD%B3%3B%C8%AB%3B%B9%A5%C2%D4&url=http%3A//www%2Ecpcwedu%2Ecom/Document/MSstudy/101239656%2Ehtm&b=0&a=9&user=baidu 网页下查看全知道了.