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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单项选择题
The Golden Gate Bridge's color is ______.
A．golden
B．green, brown and blue
C．red and orange
D．both B and C
单项选择题
The word vibrant probably means ______.
A．bright
B．soft
C．light
D．dark
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