Three containers of the same volume contain three different gases. The masses of the molecules are $m_1, m_2$ and $m_3$ and the number of molecules in their respective containers are $N_1, N_2$ and $N_3$. The gas pressures in the containers are $P_1, P_2$ and $P_3$ respectively. All the gases are now mixed and put in one of the containers. The pressure $P$ of the mixture will be

• A
  $P < (P_1 + P_2 + P_3)$
• B
  $P = \frac{P_1 + P_2 + P_3}{3}$
• C
  $P = P_1 + P_2 + P_3$
• D
  $P > (P_1 + P_2 + P_3)$