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已知则      (        )

A. B.
C. D.的夹角为

C

解析试题分析:根据题意由于,则可知,而对于,从而说明向量成立,对于D,的夹角为,故错误,对于B,由于向量的坐标不符合共线的公式,故错误,选C.
考点:向量的数量积
点评:主要是考查了向量的数量积的坐标运算属于基础题

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