Throughout history, people have been interested in knowing how languages first began, but no one knows exactly where or how this happened. However, we do know a lot about languages, the languages of today and also the languages of earlier times. There are probably about 3,000 languages in the world today. Chinese is the language with the most speakers. English, Russian and Spanish are also spoken by many millions of people. On the other hand, some languages in the world have less than one hundred speakers.
There are several important families of languages in the world. For example, most of the languages of Europe are in one large family called Indo-European. The original (最初的) language of this family was spoken about 4,500 years ago. Many of the present day languages of Europe and India are modern forms of the language of 4,500 yeas ago.
Languages are always changing. The English of today is very different from the English of 500 years ago. In time some even died out completely. About 1,000 years ago, English was a little-known relative of German spoken on one of the borders of Europe.
If a language has a large number of speakers or if it is very old, there may be differences in the way it is spoken in different areas. That is, the language may have several dialects. Chinese is a good example of
如图所示，在条形磁铁的中央位置的正上方水平固定一铜质圆环，释放圆环，则环下落时 感应电流（填产生或不产生）环下落时环的机械能 （填守恒或不守恒）
