已知則      (        )

A. B.
C. D.的夾角為

C

解析試題分析:根據(jù)題意由于,則可知,而對(duì)于,從而說(shuō)明向量成立,對(duì)于D,的夾角為,故錯(cuò)誤,對(duì)于B,由于向量的坐標(biāo)不符合共線的公式,故錯(cuò)誤,選C.
考點(diǎn):向量的數(shù)量積
點(diǎn)評(píng):主要是考查了向量的數(shù)量積的坐標(biāo)運(yùn)算屬于基礎(chǔ)題

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