单项选择题

According to the text, fossil studies of radiolaria are significant because they ______.

A．live in the depths of the ocean
B．are one-celled
C．have survived through the ages
D．demonstrate climatic changes prior to humans
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单项选择题
It can be concluded from the passage that ______.
A．the circulation of atmosphere protects the biosphere and makes life on earth possible
B．if the protective atmosphere is damaged by human activity, all life will cease
C．life is the result of complex interdependent events of nature
D．despite the complexity and power of the atmosphere humans can affect it greatly
单项选择题
According to the text, the fundamental cause of the ice ages is ______.
A．periodic changes in the earth's orbit around the sun
B．fossil remains of one-celled animals
C．alternating cold and warm seasons
D．changes in distance of the earth from the sun
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