[单项选择]When scientists first warned in the 1970s that CFCs could attack ozone, the U.S. responded by banning their use in spray cans. But the rest of the world continued to use CFC - based aerosol cans , and overall CFC production kept growing. The threat became far clearer in 1985 , when researchers reported a "hole" in the ozone layer over Antarctic. Although the size of the hole varies with the seasons and weather patterns, at times Antarctic ozone has been depleted by as much as 50% in some spots. As a result of this disturbing development, 24 nations, including the U. S. and the Soviet Union, met in Montreal two summers ago and agreed to cut back on CFCs. The so - called Montreal Protocal is designed to achieve a 35% net reduction in worldwide CFC production by 1999.
That’s not good enough, however, the same stability that makes CFC so safe in industrial use makes them extremely longlives, some of the CFCs released today will still be in the atmosphere a century from now. Moreover,
A. that CFC manufacture is completely forbidden
B. that the production of CFC is reduced
C. to find substitutes for CFCs
D. to reduce the danger of CFCs

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