We sit in the room with windows open. Then

• A

  air pressure on the floor of the room equals the atmospheric pressure but the air pressure on the ceiling is negligible
• Correct answer
  B

  air pressure is nearly the same on the floor, the walls and the ceiling
• C

  air pressure on the floor equals the weight of the air column inside the room (from floor to ceiling) per unit area
• D

  air pressure on the walls is zero since the weight of air acts downward

Hence, the correct answer is option: 'B'.