Nancy is Mr. White's little daughter. She isn't good at maths. Mr. White is teaching her, "What's four plus four?" Nancy counts (数) her fingers and answers, "It's eight." "Good. What is twenty minus three?" Nancy counts her fingers and toes. "Mm... it's five. No, it's seventeen." Nancy answers slowly. "What's eleven plus twelve, then?" Nancy looks at her fingers and toes. They are not enough (足够). Seeing this, Mr. White isn't glad arid says, "Use your head, Nancy." "That's not enough. I've got only one head."