单项选择题

What do people usually think contributed to the decline of North Africa

A．Human factors.
B．Economic factors.
C．Climatic factors.
D．Population factors.
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单项选择题
Increase in the temperature of tropical soil _______.
A．might cause the overflow of flood
B．may lead to the loss of organic nitrogen in it
C．will produce a great deal of organic nitrogen
D．is harmless to the growth of rain forests
单项选择题
From this passage we can infer that the author's attitude toward the theory of some geologists (Line 3, Para. 1) is _______.
A．approval
B．disapproval
C．indifference
D．displeasure
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