单项选择题

American scientists are very concerned about the ozone because ______.

A．the ozone is another form of oxygen
B．the ozone could keep us from the hurt from the sun's rays
C．the ozone is decreasing as a result of pollution
D．the ozone is very valuable in atmospheric research
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单项选择题
The Montreal Protocol, an international treaty, is aimed at ______.
A．restricting uses of CFC
B．restricting uses of methyl bromide
C．banning uses of CFC
D．restoring the ozone in the atmosphere
单项选择题
According to the study led by Mr. Newchurch, which of the following statements is TRUE
A．The ozone layer was increasing by 8 percent every 10 years since the late 1970s.
B．In the past few years, the decrease rate of the ozone has been steady.
C．The atmosphere is beginning to gain ozone now.
D．We'll have a full recovery of ozone in 50 years if the Montreal Protocol is well observed.
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