〔R21〕  Why is a crane like a well-known shell fish?

〔譯註〕 為何起重機像一種有名的貝殼魚？

                        註： crane 可指「鶴」或「起重機」。

〔提問〕 If the answer is “because it's an _____,” what is the right word to fill in?

〔謎底〕  h______