The Volume of a Carbon Dioxide Bubble Rising in a Glass

The volume of a carbon dioxide bubble rising in a glass of beer is observed to nearly double as the bubble rises from the bottom to the top of the glass.Why,according to our textbook,does the volume nearly double?

A) The temperature at the bottom is cooler than it is at the top.
B) The amount of carbon dioxide in the bubble increases.
C) The fluid pressure of the beer is greater at the bottom of the glass than at the top.
D) The pressure inside the bubble decreases as it rises.
E) The shape of the glass determines the net force exerted on the bubble.