点 $M(1,0,-1)$ 到直线 $L:\left\{\begin{array}{l}x-y-z+1=0, \\ x+y-2 z=0\end{array}\right.$ 的距离为
$\text{A.}$ $\frac{\sqrt{5}}{\sqrt{14}}$
$\text{B.}$ $\frac{2 \sqrt{5}}{\sqrt{14}}$
$\text{C.}$ $\frac{3 \sqrt{5}}{\sqrt{14}}$
$\text{D.}$ $\frac{4 \sqrt{5}}{\sqrt{14}}$