池塘养殖普遍存在由于饵料、鱼类排泄物、换水不及时等引起的水体污染现象，研究者设计了一

第二节：短文填词（共10小题，每小题1分，满分10分）

1.            2.            3.            4.         5.            6.             7.             8.             9.        10.

No one knows exactly how the earth began, as it happened

so long ago. However, according to a widely accepted     (理论),
the universe began with a “Big Bang” that threw matter
      all directions.  After that, atoms began to
     (形成) and combine to create stars and other bodies.
For several b     years after the “Big Bang”, the earth was
still just a cloud of dust. What it was to become w   uncertain
until between 4.5 and 3.8 billion years ago when the dust
settled into a solid     (球体) . The earth became so violent
      it was not clear whether the shape would last
      not. It exploded loudly with fire and rock. They were in
time to produce carbon, nitrogen, water vapor and other
gases, which were to make the earth’s          (大气层).
What is even more important is that as the earth   down(冷却下来),
water began to appear on its surface.
( Big Bang: 宇宙大爆炸)