His first essay was a plea for mercy to animals. Already the boy was showing that deep sympathy for the suffering which was to be so characteristic of the man.
问：which 引导的定语从句中so 的意思是？帮我剖析一下这个定语从句的成份，谢谢专家。
His first essay was a plea for mercy to animals. Already the boy was showing that deep sympathy for the suffering which was to be so characteristic of the man.
【翻译】他的第一篇文章请求对动物要怜悯。这个男生已经表现出对受难者的深切同情，这种同情心势必是他成年后所拥有的品质。
1. 这句话的难题，其实不在so 上面。so 是程度副词“这样；那样”，修饰形容词characteristic。
2. which 是关系代词，先行词是that deep sympathy（那种深切的同情）。
其他几个难题讲解：
3. a plea for：对......请求；
mercy to animals：对动物要怜悯。
a plea for mercy to animals：请求对动物要怜悯。
4. was to be：是以后时的一种表达，意为“以后注定是”。
5. be characteristic of sb.：是某人的特征；代表着某人性格或品质。
6. the man：类指“成年男子”。本句我译为“他成年后”。
