A cylindrical vessel containing a liquid is closed by a smooth piston of mass m. If A is the cross-sectional area of the piston and ${\mathrm{P}}_0$ is the atmospheric pressure, then the pressure of the liquid just below the piston is

• A

  ${\mathrm{P}}_0$

• B

  ${\mathrm{P}}_0$+$\frac{\mathrm{mg}}{\mathrm{A}}$

• C

  $\frac{\mathrm{mg}}{\mathrm{A}}$

• D

  Data is not sufficient.