a
since velocity of water coming out $=\sqrt{2 g h}$
$=\sqrt{2 \times 10 \times 5}$
$=10 \mathrm{m} / \mathrm{s}$
So volume of water $=$ velocity $\times$ area
$=10 \times 10^{-4} \mathrm{m}^{3} / \mathrm{s}$
volume flow rate $=10^{-3} \mathrm{m} / \mathrm{s}$