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______ has been ended worldwide.

A．Polio
B．Measles
C．Rubella
D．Smallpox
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热门试题

单项选择题We can infer that ______ environments help develop a person's intelligence.

A．boring
B．rich and varied
C．fixed
D．identical

单项选择题In the development of one's intelligence, environment plays ______.

A．a less important role
B．an equally important role
C．an insignificant role
D．the least significant role