If $\mathrm{D} \subseteq \mathbb{R}$ and $f: \mathrm{D} \rightarrow \mathbb{R}$ defined by $f(x)=\frac{x^2+x+a}{x^2-x+a}$ is a surjection then ' $a$ ' lies in the interval

• A

  $\mathbb{R}$
• B

  $(0, \infty)$
• Correct answer
  C

  $(-\infty, 0)$
• D

  $(0,1)$

Hence, the correct answer is option: 'C'.