The author of this text states that______.
A. the problem of obtaining good drinking water has plagued man throughout time
B. palatability is synonymous with purity of water
C. most of the world"s water is unusable as a water supply
D. man no longer depends on desalinization for his water supply
从度量机制方式划分，路由协议可以分为链路状态协议和距离向量协议。()
The authors purpose in writing this text is to argue that______.
A. the circulation of atmosphere protects the biosphere and makes life on earth possible
B. if the protective atmosphere is too 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
According to the text, fossil studies of radiolaria are possible because they______.
A. live in the depths of the ocean
B. are one-celled
C. have survived through the ages
D. have a shell surrounding the cell
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