...of which定语从句 和first of which的区别,具体如下所述

亲,您的原句应改为：Many people believe,however,that our progress depends on two aspects of science,the first of which is ...
原句存在标点符号的错误,science后面应为逗号,这样后面的定语从句才会有先行词哦!该定语从句是非限定性的定语从句,先行词为two aspects of science.
记住：非限定性定语从句有以下三种：
1）先行词,+ 关系代（副）词 + 定语从句的其它部分.
He always fails in the English exams,which makes his parents very disappointed.
2）先行词,+ 介词 + 关系代词 （which/whom）+ 定语从句的其它部分.
I don't like the man,with whom I work.
3）先行词,+ 名词（不定代词/数词）+ of + 关系代词 （which/whom）+ 定语从句的其它部分.
The old lady has three sons,two of whom are doctors.
您的这句话属于以上第三种结构.明白了吗?