TOEFL Listening: ETS-TOEFL听力机经 - ZL14S6331LU1L2H9P$

Why does the professor describe the process of petrifaction? A. To clarify the difference between bone and soft tissue B. To explain why histology can be used on dinosaur bones C. To remind students of how long ago dinosaurs lived D. To describe the origins of some cracks in dinosaur bones