单项选择题

The study of the end-Permian mass extinction is hindered by all of the following EXCEPT ______.

A．the lack of experienced researchers
B．lack of access to southern China
C．lack of relevant rock samples
D．lack of well-preserved fossils
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单项选择题
We can conclude from the passage that ______.
A．there is a consensus about the causes of the end-Permian mass extinction
B．man would not have existed without the end-Permian mass extinction
C．insects are more adaptable in coping with natural devastations
D．natural catastrophes must have hindered the evolution of life
单项选择题
The author implies that ______.
A．social agencies in America can be very helpful
B．the help to American families from social agencies is limited
C．the government should do more to improve patchwork programs
D．the fragmentary nature 6f the American family is unique
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