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푸틘 [280057] · MS 2009 · 쪽지

2011-09-26 23:03:39
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빈칸 문제 1

게시글 주소: https://dev.orbi.kr/0001785700

Two billion years ago, the Earth was completely
devoid of oxygen, and all forms of life consisted of
creatures so tiny that they would be invisible to the
human eye. Gradually, these creatures began
producing oxygen as a waste product, just as plants
do now. However, at that time, for most life, oxygen
was poisonous. As oxygen increased from 0% of our
atmosphere two billion years ago to the present
21%, species were forced to evolve. Naturally, many
species must have died in the poisonous
atmosphere. However, some managed to adapt, and
these were our ancestors. While it may seem
difficult to believe that oxygen can be poisonous to
life, this shows us _______________.
① that unpredictable results can come from
disasters
② how crucial the food chain is to all creatures'
survival
③ how rapidly we are polluting the earth
④ how essential tiny creatures are to most species
⑤ that most species would have survived with
oxygen


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