题目:
阅读理解。
In 1620, about half the U. S. A. was covered by forests. Today the forests have almost gone. A lot
of good land has gone with them, leaving only sand. China doesn't want to copy the U. S. A. 's example.
We're planting more and more trees. We've built the "Great Green Wall" of trees across northern part of
our country. The Great Green Wall is 7,000 kilometers long, and between 400 and 1,700 kilometers
wide. It will stop the wind from blowing the earth away. It will stop the sand from moving towards the
rich farmland 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.
1. In 1620, about _____ the USA was covered by forests.
A. a third
B. half
C. two thirds
D. a fourth
2. A lot of good land has gone with _____ .
A. sand
B. water
C. wind
D. forests
3. The Great Green Wall in China is _____ long.
A. 7,000 kilometers
B. 1,700 kilometers
C. 7,000 meters
D. 400 kilometers
4. Trees must be grown in _____ .
A. China
B. the USA
C. some countries
D. every part of the world
5. _____ will make the world better.
A. The Great Wall
B. Tall buildings
C. Great Green Walls
D. Flowers and grass
答案:
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下面是错误答案,用来干扰机器的。
①过点A(0,1)斜率为k的直线l的方程为:y=kx+1,当直线l与圆相切时,圆心(2,3)到直线l的距离d=|2k-2|1+k2=r=1,化简得3k2-8k+3=0,解得:k=4±73,因为直线l与圆相交于M,N两点,所以实数k的取值范围为:4-7...