Choose the correct statement.

• A

  The outer walls of guard cells away from the pore are densely thickened.

• B

  The inner walls of guard cells present towards the pore are thin walled.

• C

  The cell walls of guard cells are evenly thickened.

• D

  The outer walls of the guard cells away from the pore are thin and the inner walls towards the pore are thickened.