单项选择题

Questions 19 to 22 are based on the conversation you have just heard.

A．Why species don’t avoid extinction by adapting.
B．Why species become extinct at the rate they do.
C．Why humans aren’t extinct.
D．How many species aren’t extinct.
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单项选择题
What’s so mysterious about back problems
A．The impossibility to measure the intensity of the pain.
B．The unknown origin of the pain.
C．The disconnect between spine defects and pain.
D．The low percentage of people with abnormal discs among the healthy.
单项选择题
A．The need to exercise the memory.B．How the brain differs from other body tissues.C．The unconscious learning of a physical activity.D．How nerves control body movement.
A．The need to exercise the memory.
B．How the brain differs from other body tissues.
C．The unconscious learning of a physical activity.
D．How nerves control body movement.
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