TOEFL Listening: ETS-TOEFL听力机经 - 4SPGL_1URVC64186P$

What is the main purpose of the lecture? A. To point out the flaws in a newly proposed theory B. To describe a new understanding of a basic process in soil hydrology C. To address concerns about using stable isotope analysis D. To provide an explanation of a study described in the class's textbook