As you read the excerpt below, think about how the author has organized or structured the information. Think of a bottle of soda pop. Before it is opened, there is no sign of bubbles. As soon as the bottle is opened, though, bubbles suddenly appear. In fact, they can foam all over the place. That is because there is a gas, carbon dioxide, dissolved inside the liquid soda. The soda in the closed bottle is under pressure. When a liquid is under pressure, it can dissolve more gas than when it is not under pressure. As soon as you open a bottle, there is less pressure inside it, and it cannot dissolve as much gas. That makes gas bubbles form as the gas tries to expand.

What best describes the structure of the paragraph?
A. a problem and its solution
B. an explanation of a process
C. a sequence of events
D. compare and contrast