单选题 The author mentions the eruption of Mount St. Helens (lines 25 - 26) primarily in order to emphasize which of the following points?

• (A) The deep and enduring effect that volcanic eruptions have on the environment
• (B) The process by which classic volcanic eruptions tend to occur
• (C) The relative dearth of cases with scientists can judge the effects of volcanic eruptions
• (D) A sample case with which later volcanic explosions are compared
• (E) The global cooling effects of one of the best-studied volcanic eruptions