根据《混规》第 11.7.9 条

$$ l _ {\mathrm{n}} / h = 2. 5 / 0. 9 = 2. 7 8 > 2. 5 $$

$$ h _ {0} = 9 0 0 - 7 0 = 8 3 0 \mathrm{mm} $$

$$ V _ {\mathrm{wb}} \leq \frac {1}{\gamma_ {\mathrm{RE}}} (0. 2 0 \beta_ {\mathrm{c}} f _ {\mathrm{c}} b h _ {0}) = \frac {1}{0 . 8 5} \times (0. 2 \times 1. 0 \times 1 9. 1 \times 4 0 0 \times 8 3 0) = 1 4 9 2 \mathrm{kN} $$

根据《混规》第 11.7.8 条

9度设防烈度的一级抗震等级连梁

$$ M _ {\mathrm{bua}} = \frac {1}{\gamma_ {\mathrm{RE}}} f _ {\mathrm{yk}} A _ {\mathrm{s}} \left(h _ {0} - a _ {\mathrm{s}} ^ {\prime}\right) $$

$$ V _ {\mathrm{wb}} = 1. 1 \times \frac {M _ {\mathrm{bua}} ^ {l} + M _ {\mathrm{bua}} ^ {\mathrm{r}}}{l _ {\mathrm{n}}} + V _ {\mathrm{Gb}} = 1. 1 \times \frac {\frac {1}{0 . 7 5} \times 4 0 0 \times A _ {\mathrm{s}} \times (8 3 0 - 7 0) \times 2}{2 5 0 0} + 0 \leqslant 4 9 2 \times 1 0 ^ {- 3} $$

$$ A _ {\mathrm{s}} \leq 4 1 8 2. 9 \mathrm{mm} ^ {2} $$

因此选（B）