已知E(X)=2，E(Y)=2，E(XY)=4，则X，Y的协方差Cov(X,Y)=（）.-湖北继续教育网网校

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[单选题]已知E(X)=2，E(Y)=2，E(XY)=4，则X，Y的协方差Cov(X,Y)=（）.

A1b.2c.3d.4

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