句子结构分析However,itwasn'tuntilthediscoveryofthereactionprinciple,whichwasthekeytospacetravelandsorepresentsoneofthegreatmilestonesinthehistoryofscientificthought,thatrockettechnologywasabletodevelop.itwasn'

Question

句子结构分析
However,it wasn't until the discovery of the reaction principle,which was the key to space travel and so represents one of the great milestones in the history of scientific thought,that rocket technology was able to develop.
it wasn't 的表语在哪里?
出自剑桥3 test1 阅读 section1
我知道这是强调句，但是强调句通常会有个表语，比如:
It was you who broke the law.其中you就是表语。It was on Monday night that all this happend.其中 on Monday night 是表语。而我问的这个句子比较特别：
It wasn't ( ) untill the discovery of the reaction principle,that rocket technology was able to develop.
如果可以这样用的话我们就可以举一反三了：
It wasn't untill the finish of all the courses,that I was able to pass the exam.
如果把前面两个句子变成简单的正序：
Rocket technology wasn't able to develop untill the discovery of the reaction principle.
I was not able to pass the exam untill the finish of all the courses.

Answer 1

中间插入了一个定语从句
本来是这样的
it wasn't until the discovery of the reaction principle that rocket technology was able to develop.
看出来了吧 这是一个not...until的强调句