The Pitot tube shown in the figure is used to measure fluid flow velocity in a pipe of cross-sectional area $S$. It was invented by a French engineer Henri Pitot in the early $18^{th}$ century. The volume of the gas flowing across the section of the pipe per unit time is (The difference in the liquid columns is $\Delta h$,$\rho_0$ and $\rho$ are the densities of liquid and the gas respectively):

• A
  $Q = 2S\sqrt{\frac{\Delta h \rho_0 g}{\rho}}$
• B
  $Q = S\sqrt{\frac{2\Delta h \rho_0 g}{\rho}}$
• C
  $Q = S\sqrt{\frac{\Delta h \rho_0 g}{\rho}}$
• D
  $Q = S\sqrt{\frac{2\Delta h \rho g}{\rho_0}}$