单项选择题

A considerable amount of time and money has been invested in______this system.

A．defining
B．implying
C．reducing
D．perfecting
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单项选择题
The Untied States and Canada are lands of______except for the Indians, who are the only true natives.
A．emigrants
B．immigrants
C．dwellers
D．inhabitants
单项选择题
Americans are highly______, and therefore may find it difficult to become deeply involved with others.
A．moving
B．mobile
C．movable
D．motional
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