Which statement about birds is true?

Which statement about birds is true?

• A. They are non-vertebrates.
• B. They have gills.
• C. They lack a beak.
• D. They have feathers, a beak, and typically lack teeth.

Answer: (D)

Birds are vertebrates with feathers, a defining trait that sets them apart from invertebrates. They also have a beak, and in modern species they typically lack teeth. Their breathing relies on lungs with air sacs, not gills. Putting these ideas together, the statement that birds have feathers, a beak, and usually no teeth describes their biology accurately. (Note that some ancient birds did have teeth, but today’s birds do not.)