Frank’s uncle gave him a riddle (谜语) to solve: “What has 1 legs, no back, arms, or head, and you sit on it?” Frank looked around his house, searching for a 2 answer. In his room, he had a 3 , which had four legs. It had a headboard (床头板), which was like a head, and he didn’t really sit on it so much as lay down. In the living room, the sofa was strikeout (出局) 4 the backs and arms. What exactly was there left in his house that fit the description? He looked more, walking past his sister’s room, and his parents’ room. Still, 5 worked as an answer. This was hard! What 6 it be?