单项选择题

No one knows how man learned to make words. Perhaps he began by making sounds like those made by animals. Perhaps he grunted like a pig when he lifted something heavy. Per-haps he made sounds like those he heard all round him--water splashing, bees humming, a stone falling to the ground. Somehow he learned to make words. As the centuries went by, he made more and more new words. This is what we mean by language. People living in different countries made different kinds of words. Today there are about fif-teen hundred different languages in the world. Each contains many thousands of words. A very large English dictionary, for example, contains four or five hundred thousand words. But we do not need all these. Only a few thousand words are used in everyday life. The words you know are called your vocabulary. You should try to make your vocabulary big-ger. Read as many books as you can. There are plenty of books written in easy English for you toread. You will enjoy them. When you meet a new word, find it in your dictionary. Your dictiona-ry is your most useful book. You can enlarge your vocabulary by__________.