A triangular lamina of area A and height h is immersed in a liquid of density $\mathrm{\rho }$  in a vertical plane with its base on the surface of the liquid. The thrust on the lamina is

• A

  $\frac{1}{2}\mathrm{A} \mathrm{\rho gh}$

• B

  $\frac{1}{3}A \rho gh$

• C

  $\frac{1}{6}A \rho gh$

• D

  $\frac{2}{3}A \rho gh$