TOEFL Listening: ETS-TOEFL听力机经 - UFQ7Y309E3VKT4NTP$

Why does the professor mention sulfur dioxide when he discusses the 1991 eruption of Mount Pinatubo? A. To illustrate the large increase in gas emissions that can precede a volcanic eruption. B. To demonstrate an advantage of continuous monitoring of active volcanoes. C. To point out that hot springs near volcanoes typically release sulfur dioxide. D. To make a general point about the consequences of volcanic eruptions.