帮忙解释一下这句的结构

帮忙解释一下这句的结构
原句：perhaps most challenging is the set of skills required to produce a written assignment,the most common means by which student learning is evaluated.
请问逗号以后的部分与前句是什么结构关系啊?并请翻译一下,谢谢!

perhaps most challenging (thing)做主语,IS 谓语,the set of skills 表语,required to produce a written assignment做skills的后置定语,the most common means做the set of skills required to produce a written assignment的补语,但又有点像同位语
可能最大的挑战就是一系列写文章所需的技能,一种评价学生学习的最寻常的方式