单项选择题

A．Environmental changes must have caused the end-Permia……

Which of the following is TRUE

A．Environmental changes must have caused the end-Permian mass extinction.
B．Massive volcanic eruptions might have caused the end-Permian mass extinction.
C．The disappearance o dinosaurs was a consequence of the end-Permian mass extinction.
D．Marine animals appeared as a result of the end-Permian mass extinction,

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单项选择题What distinguishes the end-Permian mass extinction from other similar devastations

A．Change of ocean chemistry.
B．Survival of Miocidaris.
C．Causes.
D．Ecological reorganization.

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

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

单项选择题What is said to be the major problem facing young couples

A．They need to fulfill more duties.
B．They are incapable of balancing the budget.
C．They have their children spoiled and overindulged.
D．They get empty-handed after divorc