Schools in the east tend to be better equipped, those in the west are relatively poor.A.

Schools in the east tend to be better equipped, those in the west are relatively poor.
A. As
B. While
C. When
D. But

A. As(答案→)B. WhileC. WhenD. But解析：考查连词。While然而；句意：东部的学校有更好的设备，然而西部的学校却相贫穷。

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