TOEFL Listening: ETS-TOEFL听力机经 - 4B4G29F73PS4FV1JP$

What is the lecture mainly about? A. How the Atlantic Ocean became connected to the Arctic Ocean B. How changes in ocean circulation affected the Isthmus of Panama C. How the formation of the Isthmus of Panama helped start an ice age D. How tectonic plate movement might have created the Gulf Stream