根据《地处规》第7.1.5条

$$ m = \frac {d ^ {2}}{d _ {\mathrm{e}} ^ {2}} = \frac {0 . 4 ^ {2}}{(1 . 1 3 \times 2) ^ {2}} = 0. 0 3 1 3 $$

$$ \beta = \frac {f _ {\mathrm{spk}} - \lambda m \frac {R _ {\mathrm{a}}}{A _ {\mathrm{p}}}}{(1 - m) f _ {\mathrm{sk}}} = \frac {2 3 0 - 0 . 0 3 1 3 \times 5 7 0 / \left(\frac {1}{4} \times 3 . 1 4 \times 0 . 4 ^ {2}\right)}{(1 - 0 . 0 3 1 3) \times 1 0 0} = 0. 9 0 7 $$

因此选（C）。