During the Spring and Autumn Period, the agricultural production was highly subject to the seasonal changes with the invention of iron tools, thus forming the concept of Solar Term.
春秋战国以后随着铁制农具的出现，农业生产对季节性的要求更高了，就逐渐形成了节气的概念。
The concept of adding iron to the ocean dates to at least 1990.
向海中添加铁这一观点至少可追溯到1990年。
"Iron house" refers to the space form of character's concept.
“铁屋”是人物观念的空间形式。
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