A：$\forall x\in R,x^2-x+\frac{1}{4}<0$

B：$\forall x\notin R,x^2-x+\frac{1}{4}<0$

C：$\exists x\notin R,x^2-x+\frac{1}{4}<0$

D：$\exists x\in R,x^2-x+\frac{1}{4}<0$