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  3. The Ozone Layer, found in the stratosphere between 10km and【M10】km above the ground, protects earth from the harmful effects of

The Ozone Layer, found in the stratosphere between 10km and【M10】km above the ground, protects earth from the harmful effects of

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问题    The Ozone Layer, found in the stratosphere between 10km and【M10】km
above the ground,  protects earth from the harmful effects of certain【M1】______
wavelength of ultra-violet (UV) light from the sun, specifically UV-B.【M2】______
Any significant decrease in ozone in the stratosphere would result from an【M3】______
increase of UV-B radiation reaching the earth surface.
   Scientists warned for decades that increases in levels of UV-B【M4】______
radiation must cause the increase in skin cancers.      【M5】______
   An Antarctic "ozone hole" was discovered in 1985.  Since then,
scientists have observed ozone depletion in the middle and higher latitudes.
   This year, the biggest ozone hole even recorded was observed over 【M6】______
Antarctica, expanding over the southern tip of South America.  【M7】______
   To halt ozone depletion, countries committed themselves to ban the use【M8】______
and production of CFCs through implementation of the 1987 Montreal Protocol.
    According to data received from the Cape Grimm Global Atmosphere
Monitoring Station locating in Australia, which measures worldwide CFCs【M9】______
in the lowest layer of the atmosphere, the most common CFCs, such as
like Freon used in refrigeration, have reached zero growth.   【M10】______
This means that these substances are not increasing in concentrations
on the earth’s surface. Less common CFCs have begun to decrease in the
last two years.
【M4】
选项
答案Scientists∧warned—加入have
解析 因为有for decades，所以要用现在完成时。
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