What is a ring species and what makes it challenging for the species concept?

What is a ring species and what makes it challenging for the species concept?

• A. A chain of interbreeding populations where end populations cannot interbreed, complicating discrete species boundaries
• B. A chain of interbreeding populations where end populations can interbreed, making species boundaries clear
• C. A species found in a ring-shaped habitat
• D. A theoretical model with no real-world examples

Answer: (A)