The diagram below shows a hand warmer. It uses a controlled burn of a type of lighter fluid called naphtha.



The device has a refillable reservoir that holds the naphtha liquid. The fuel moves into a glass fiber burner, which absorbs the fuel and allows it to burn slowly without producing a flame. Oxygen reaches the burner through the holes on the cap at the top of the device. As the fuel is burned, heat is conducted to the metal casing of the device.

When the hand warmer is tested, it becomes too hot and uncomfortable to hold. How could the device be modified to solve this problem?
A.
by increasing the size of the fuel reservoir so that it can store more liquid fuel
B.
by replacing the glass fiber burner with a material that does not soak up liquid fuel
C.
by attaching a covering to reduce the amount of oxygen entering the device
D.
by using a fuel that is more flammable than naphtha so that the fuel can be used faster