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【3年随心畅学班】》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~
If it had not been for 这里it是形式主语，没有所指的。
这个短语的意思是“要不是……”

Everyone agrees that it was your quick-witted response in that emergency that has led to this satisfactory outcome.
这里it was…that…构成了强调句，“正是……”，在这里对your quick-witted response in that emergency进行强调。
其中it was…that不作成分，句子的本质是Everyone agrees that your quick-witted response in that emergency has led to this satisfactory outcome.
这两种表达意思不同：
Everyone agrees that your quick-witted response in that emergency has led to this satisfactory outcome.  大家都认为你在紧急情况下的快速反应导致了这一令人满意的结果。
Everyone agrees that it was your quick-witted response in that emergency that has led to this satisfactory outcome. 大家都认为，正是你在紧急情况下的机智反应导致了这一令人满意的结果。

可以在这里看看英语强调句的用法和构成
https://www.hjenglish.com/new/p621982/


祝同学学习进步~