When a pressure cooker is half filled with water, and heated to boiling point, then the pressure inside the cooker will?

• A decrease, since only a fraction of the water molecules has changed to vapour
• B remain constant, because the total number of water molecules has not changed
• C increase, because the water molecules can now reach every part of the sealed tube
• D decrease, since water boils under reduced pressure
• E increase, because the water vapour molecules now strike the walls of the tube more frequently because of their increased velocity