若集合 $M=\left\{x \left\lvert\, x^{\frac{1}{2}} < 9\right.\right\}, N=\left\{x \mid x^2 \geq 1\right\}$ ，则 $M \cap N=(\quad)$
$\text{A.}$ $\{x \mid x \leq-1$ 或 $1 \leq x < 3\}$
$\text{B.}$ $\{x \mid 1 \leq x < 3\}$
$\text{C.}$ $\{x \mid 1 \leq x < 81\}$
$\text{D.}$ $\{x \mid x \leq-1$ 或 $1 \leq x < 81\}$
$\text{E.}$
$\text{F.}$