If x is real, then the minimum value of $\large\frac{x^2-x+1}{x^2+x+1}$, is :

Question

$$\begin {array} {1 1} (a)\;\frac{1}{3} & \quad (b)\;3 \\ (c)\;\frac{1}{2} & \quad (d)\;1 \end {array}$$