TOEFL Listening: TPO-TOEFL听力TPO - KHY7M02DISSYG02YR$

Why does the professor say this: A. To let students know that the term "greenhouse effect" will be tested B. To indicate that the definition of "greenhouse effect" will be discussed C. To suggest that his previous definition of "greenhouse effect" was imprecise D. To acknowledge that there is controversy surrounding the use of the term "greenhouse effect"