人教版（新课程标准） 必修4 Unit 2 Working the land课时作业含解析（7份打包）.zip

Unit 2 Working the land
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People can't survive without food. Long ago, early people couldn't grow crops, so they had to live by hunting animals and gathering grains. After a tribe (部落) had lived in an area for some time, its food supply would begin to reduce. Then the tribe had to move to new hunting grounds where there was more food.
This way of life caused special problems for the tribes. They were forced to depend on luck, as well as on their hunting skills. If they could find no game, the whole tribe would be in danger of starving. And when the hunters had good luck one day, they were not sure to find game the next time. The tribes moved often because much land was needed to support their people.
As time passed by, people learned that they could grow their food. At first, the women of tribes collected patches of wild grain. Later, people discovered that they could plant their own seeds. Farming slowly became a way of life.
As people turned away from hunting to farming, their life changed. When the food supply became richer and richer, they no longer moved from place to place. The success of their crops depended partly on the weather, but there were also things they could do to help crops grow.
In the past, a tribe had to travel many miles for food. Now, only a small amount of land was necessary to feed the whole tribe. The early tribe could grow in size beca