In 1620, about half the USA was covered(覆盖) by forests. Today the forests have almost gone. A lot of good land has gone with them, leaving only sand(沙地). China doesnt want to copy(抄) the USAs example. Were planting more and more trees. Weve built the Great Green Wall of trees across northern(北部的) part of our Great Green Wall is 7,000 kilometres long, and between 400 and 1,700 kilometres wide. It will stop the wind from blowing the earth away. It will stop the sand from moving towards the rich farmland(农田) in the south. More Great Green Walls are needed. Trees must be grown all over the world. Great Green Walls will make the world better.
根据短文内容，选择正确答案。
1620, about ______ the USA was covered by forests.
A.a third thirds D.a fourth
2.A lot of good land has gone with ______.
r sts
Great Green Wall in China is ______ long.
A.7,000 kilometers B.1,700 kilometers
C.7,000 meters D.400 kilometers
s must be grown in ______.
a USA countries y part of the world
5.______ will make the world better.
Great Wall buildings
t Green Walls ers and grass
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