Three people—call them Al, Bob, and Cary—were standing together at a bus stop. A stranger asked Al, “Are you a knight or a knave?” Al answered, but the stranger could not make out what he said. The stranger then asked Bob, “What did Al say?” Bob replied, “Al said that he is a knave.” At this point, Cary said, “Don’t believe Bob; he is lying!” What are Bob and Cary?

In a certain kingdom, there were knights and knaves. The knights always tell the truth and the knaves always lie. Everyone in the kingdom is either a knight or a knave. Use this information to answer the questions in Problems 21–24.