同学你好，该知识点来自沪江网校《英语零基础直达大学六级【开学季特惠班】》的课程，想要更系统的学习，欢迎进入课程学习。不仅可以和更多的同学一起学习，而且还有老师、助教随时的学习指导和知识点解答哦。

同学你好~
It is very difficult to describe my happiness in words.
it是形式主语，to describe my happiness是不定式短语作真正的主语
is是系动词作谓语
very difficult是表语
in words 状语
这个句子相当于 To describe my happiness in words is very difficult.

in words 用语言
Man thinks in words.
人类的思维是凭藉语言来进行的。

祝同学学习进步~