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命题" $\forall x>0, x^2-x+1>0$ "的否定为
A. $\forall x>0, x^2-x+1 \leq 0$     B. $\forall x \leq 0, x^2-x+1 \leq 0$     C. $\exists x>0, x^2-x+1 \leq 0$     D. $\exists x \leq 0, x^2-x+1 \leq 0$         
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