单项选择题

Animal migration is a seasonal or periodic movement of animals in response to changes in climate or food ______, or to ensure reproduction.

A．alternation
B．availability
C．utilization
D．capacity
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单项选择题
By dint of much practice, he became ______ and was able to sign his name with either hand.
A．practical
B．tricky
C．ambiguous
D．ambidextrous
单项选择题
During the late 1950s, the Brazilian economy ______ forward as heavy industries and basic infrastructure--roads, communications, and construction--expanded.
A．increased
B．splashed
C．surged
D．improved
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