$A$ poly-atomic molecule $(C_v = 3R, C_p = 4R$,where $R$ is the gas constant) goes from phase space point $A (P_A = 10^5 \ Pa, V_A = 4 \times 10^{-6} \ m^3)$ to point $B (P_B = 5 \times 10^4 \ Pa, V_B = 6 \times 10^{-6} \ m^3)$ and then to point $C (P_C = 10^4 \ Pa, V_C = 8 \times 10^{-6} \ m^3)$. The path $A$ to $B$ is adiabatic and the path $B$ to $C$ is isothermal. The net heat absorbed per unit mole by the system is:

• A
  $500 R (\ln 3 + \ln 4)$
• B
  $450 R (\ln 4 - \ln 3)$
• C
  $500 R \ln 2$
• D
  $400 R \ln 4$