If $f\left(x\right)=\left\{\begin{array}{l}x, x \mathrm{isrational}\\ 1-x, x \mathrm{irrational}\end{array}\right.$ Then $f\left(f\left(x\right)\right)$ is

• A

  $x\forall x\in R$

• B

  $\left\{\begin{array}{l}x, x \mathrm{is} \mathrm{irrational}\\ 1-x, x \mathrm{is} \mathrm{rational}\end{array}\right.$

• C

  $\left\{\begin{array}{l}x, x \mathrm{is} \mathrm{rational}\\ 1-x, x \mathrm{isirrational}\end{array}\right.$

• D

  none of these