Millions of years ago, dinosaurs (恐龙) lived on earth. At that time, the whole earth was warm and wet. There were green forests and they could find enough to eat.
Gradually(渐渐地), parts of the earth became cold and dry and the forests there died. Then dinosaurs could not find enough to eat. This must be one reason why dinosaurs died out (灭绝).
There may be other reasons that we do not yet know about. Scientists are trying to make more discoveries(发现)about dinosaurs.
We now know that dinosaurs were of many sizes and shapes. Some were as small as chickens, while some were about 90 feet long.
There were also terrible fights(战争)between dinosaurs! They might have happened more than 100 millions years ago. Though no man was there to see any of the fights, we can tell by the animals’ footprints that fights did happen.
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