TOEFL Listening: TPO-TOEFL阅读TPO - 35DQ5E5QO12WL743N$

The period discussed in the passage is referred to as an "explosion" because it A. occurred 0.6 billion years ago, late in Earth's history B. was characterized by the unusually fast evolution of many new life-forms C. was characterized by widespread animal extinction D. was characterized by violent volcanic eruptions