TOEFL Listening: ETS-TOEFL听力机经 - 9B4J3SKA4P9J9364P$

What is the lecture mainly about? A. A method that is used to determine an animal's diet B. How scientists determine where migratory birds stop to feed C. The different forms of carbon that can be found in animals D. How migratory birds find different types of food at stopover sites