The ratio of the specific heat capacities of a gas is $1.5$. When the gas undergoes an adiabatic process, its volume is doubled and pressure becomes $P_1$. When the gas undergoes an isothermal process, its volume is doubled and pressure becomes $P_2$. If $P_1 = P_2$, the ratio of the initial pressures of the gas when it undergoes adiabatic and isothermal processes is

• A
  $\sqrt{3}: \sqrt{2}$
• B
  $1: 1$
• C
  $\sqrt{3}: 1$
• D
  $\sqrt{2}: 1$