Read this excerpt from "Marine Mammals.” Marine mammals are classified into four different groups: cetaceans (whales, dolphins, and porpoises), pinnipeds (seals, sea lions, and walruses), sirenians (manatees and dugongs), and marine fissipeds (polar bears and sea otters)

–"Marine Mammals,"
National Oceanic and Atmospheric Administration

Which best describes how the author’s use of classification helps to guide the reader’s understanding?

A. It provides details about marine mammals.
B. It is used to define the types of marine mammals.
C. It divides the larger topic of marine mammals into smaller parts.
D. It allows the author to provide a description of each type of marine mammal.