Read the passage from "A World Of Animals.” There are more than a million types of animals on our planet, but most of them belong to one of only six main groups. These six groups are mammals, reptiles, birds, invertebrates, fish, and amphibians. Each group has millions of these different types of animals, with each type sharing the same characteristics. For example, mammals all have hair on their bodies, are warm-blooded, and have backbones, or spines. Mammals give birth to live babies rather than lay eggs. In the mammal group, there are more humans than any other type of animal. Humans number seven billion people. One main idea of the paragraph is that animals in the same group share characteristics. Which detail supports the main idea?
