这句定语从句中,为什么用了in which,分析句子成分

问题描述:

这句定语从句中,为什么用了in which,分析句子成分
I hit upon an article in which some people hold that students should wear uniforms every day.

in which就是in the article
"some people hold that students should wear uniforms every day"作定语,这个观点是在文章里的,所以加in.
句子主干就是I hit upon an article.