单项选择题

The passage mainly talks about ______.

A．the effect of diseases
B．how to control the number of certain animals
C．the relationship between diseases and human population
D．different kinds of diseases
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单项选择题
The relative stability of the human population has been upset by ______.
A．the proportion of the reproductive age group
B．the influenza epidemic
C．advances in medical science
D．the Black Death in Europe
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