Water vapour comes out from the plant leaf through the stomatal opening. Through the same stomatal opening,carbon dioxide diffuses into the plant during photosynthesis. Reason out the above statements using one of the following options.

• A
  The above processes happen only during night time.
• B
  One process occurs during day time and the other at night.
• C
  Both processes cannot happen simultaneously.
• D
  Both processes can happen together because the diffusion coefficient of water and $CO_2$ is different.