Explanation: Analogy After a long exercise, become very strong. Usage: -Linked; as the predicate attribute; metaphor not afraid of failure, strong-willed Source: Guo Xiaochuan "defend our party" poem: "lit the fire of struggle, people tempered into a steel in the fire." Examples: Practice of the younger generation only through the various tests in order to ~. Results: Iron furnace Postscript: Iron furnace