题目内容
(请给出正确答案)
[单选题]
下列式子可出现负值的是()
A.Σ(X-SPAN style“TEXT-DECORATION overline“X/SPAN)2
B.Σ(Y-SPAN style“TEXT-DECORATION overline“Y/SPAN)2
C.Σ(X-SPAN style“TEXT-DECORATION overline“X/SPAN)(Y-SPAN style“TEXT-DECORATION overline“Y/SPAN)
D.ΣX2-(ΣX)2/n
E.ΣY2-(ΣY)2/n
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