google ai:
The riddle, "A man has two, a king has four, and a beggar has none," refers to the letter "A" in the words "man," "king," and "beggar".
Man: Has two "a"s (m-a-n-k-i-n-g).
King: Has four "a"s (king).
Beggar: Has no "a"s (beggar).
This is a common word riddle that plays on the letters within the words themselves rather than their meanings.