一道语法填空试题
People 1_________ （live） in different countries made different kinds of words. Today there are about fifteen hundred 2_________ in the world. Each contains many thousands of words. A very large dictionary, for example, contains four 3_________ five hundred thousand words. But we do not need 4_________ these. To read short stories you need to know only about two thousand words. 5_________ you leave school, you will learn only one thousand or more.
The words you know are called your vocabulary. You should try to make your vocabulary 6__________ （big）. Read as many books as we can. There are a lot of books 7__________ （write） in easy English. You will enjoy them. When you meet 8_________ new word, look it 9_________ in your dictionary. Your dictionary is your 10__________ （much） useful book.
第5个空为什么填before而不填when,我觉得when更加适合,解释一下,谢谢!