Consider a gas with density \[\rho \] and \[\bar{c}\] as the root mean square velocity of its molecules contained in a volume. If the system moves as whole with velocity v, then the pressure exerted by the gas is

• A. \[\frac{1}{3}\rho \,{{\bar{c}}^{2}}\]
• B. \[\frac{1}{3}\rho {{(c+v)}^{2}}\]
• C. \[\frac{1}{3}\rho {{(\bar{c}-v)}^{2}}\]
• D. \[\frac{1}{3}\rho {{({{c}^{-2}}-v)}^{2}}\]