Final answer:
The sentence from the Yellowstone description pointing out its unique volcanic features and wildlife supports the author's claim about the uniqueness of the United States' natural features.
Step-by-step explanation:
The sentence that supports the author's claim that the United States' natural features are like no others in the world is: The Yellowstone outranks by far any similar volcanic area in the world. It contains more and greater geysers than all the rest of the world together; the next in rank are divided between Iceland and New Zealand. Its famous canyon is alone of its quality of beauty. Except for portions of the African jungle, the Yellowstone is probably the most populated wild animal area in the world, and its wild animals are comparatively fearless, even sometimes friendly.