赤道地区全年高温多雨，南极大陆终年严寒少雨，导致两地气候差异的主要因素是：（）

       Can you remember the day when you spoke your first word? If you can, you are unusual.
       Try to imagine what first few months of your life were like. I am sure you just spent most of your time
eating, sleeping and crying. As you grew older, you were awake more of the time. It took your parents more
time to play with you and talk to you. You watched and listened curiously (好奇). You began to know that
people made certain sounds to go with certain things.
       Then you began to try making the sounds you heard. And step by step you were able to make the right
sound for one thing.
       On that day you came to understand the secret of language. The secret is that a certain sound means a
certain thing. One sound might be as good as another. But it is no good as a word unless everybody agrees
on its meaning. Only when a group of people use the same set of sounds of things, can they understand each
other. Then, and only then do these people have a LANGUAGE.
       After you found the secret of language, you learned words. Some of the words meant things, such as
BOOKS, CHAIRS and SHOES. Some words meant doing things, such as GO and SWIM, and other words
describe things, such as GOOD and DIRTY. Soon you learned to put words together to express your idea,
such as "I want to go out and play with my friends." This is language. By means of language people can
communicate (交流). So we say languages are means of communication.