TOEFL Listening: ETS-TOEFL听力机经 - P87YDXDTAD5P62ZEP$

What is the main purpose of the lecture? A. To explain why volcanic eruptions are predictable but earthquakes are not. B. To describe changes that help scientists predict volcanic eruptions. C. To compare the recent eruptions of Mount St. Helens and Mount Pinatubo. D. To discuss four types of instruments designed to predict volcanic activity.