人教版高一英语上09

[06:18.54]The answer is this:you can only grow crops in the forest for one or two years.
[06:26.27]The soil is very thin in the forest.
[06:30.40]It is only about 20 centimetres thick.
[06:35.08]It can easily be destroyed by the burning and by the cows.
[06:41.03]They soil is made from the dead leaves of the trees above.
[06:46.18]Under the soil there is nothing but sand.
[06:50.83]When this soil is destroyed,the forest land will become sand again.
[06:57.20]But this time there will be no trees to make new soil from their leaves.