TOEFL Listening: ETS-TOEFL听力机经 - 93L78FBP1L13V95GP$

What is the main topic of the lecture? A. The three distinct parts of nutrient absorption in unicellular organisms B. Differing forms of three general stages of the digestive process C. Why larger organisms require more complex digestive processes than protozoa D. Differences among the digestive processes of amoeba, paramecia, and other protozoans