One day, a group of small fish were playing in the pond. It happened that a duck was swimming in the pond. The duck saw the fish and thought, I'm hungry. There are a few small fish, so fill them with small fish. Thinking about it, I swallowed a small fish. "Oh, it's delicious! Then I will eat a few more. " Said the duck. As a result, all the small fish became a delicious meal for ducks. This afternoon, the fish called a meeting to discuss this problem-how to stop the duck's attack. This question is very difficult, and the fish thinks hard and still can't figure it out. At this moment, a fish nicknamed "Little Clever" suddenly said, "I have an idea!" All the other fish asked, "What can I do?" "Smart" said, "My way is to tie a bell on the duck's foot. As soon as he swam over, the bell rang and we knew. " The fish applauded. An experienced fish did not say a word. Later, he said: "The clever method is really good, but there is still a small problem to be solved, that is, who tied the bell on the duck's foot?" The fish (including Xiaoling) were silent. It may seem easy to come up with a good idea, but it is not so easy to do it. ?