TOEFL Listening: ETS-TOEFL听力机经 - 3L1YTJR3Y9D3_31OP$

What are two characteristics of bio-film that help explain the feeding behavior of some shore animals? A. It is found on the surface of shoreline mud. B. It is produced by mud snails and clams. C. It consists mainly of tiny crustaceans. D. It has a high carbohydrate content.