The diagram above illustrates trapped air in a syringe placed in water that is gradually heated. It is observed that the piston rises as the temperature of the water rises. Which of the following statements explains this observation?

• A.frequency of collision of trapped air molecules with walls of the syringe is more
• B.molecules of trapped air expands more
• C.speed of the trapped air molecules decreases
• D.number of molecules of trapped air increases