Question

英语语法：请从语法角度分析这个句子的结构

I think I had at least a billion test, including one in which they cut out a piece of muscle from my leg and looked at it under a microscope.

Answer 1

I think I had at least a billion test, including one in which they cut out a piece of muscle from my leg and looked at it under a microscope.

这个句子的意思的：我觉得我至少经历了十亿次考验了，包括曾经有一次他们从我的腿上切下了一块肉，并放在显微镜下让我观察。

这是一个非限定性定语从句。定语从句前有逗号隔开的是非限定性定语从句标志。
I think是插入语，就是省略了I think，也不影响这个句子要表达的主要意思。
I had at least a billion test，I 就是主语，had就是谓语， test就是宾语。
at least a billon是修饰test的，可作定语。
然后右面的including这一句，就是介词短语做定语，继续修饰说明test。
怎样的test呢，就是they cut out a piece of muscle from my leg and looked at it under a microscope。
including one in which they cut out a piece of muscle from my leg and looked at it under a microscope。在整个句子中是做从句的，从句中的主语是one，which是引导词，in在这里是在....中的意思，不能省略，还原句子就是including in one test，they cut out a piece of muscle from my leg 。。。。。翻译成中文就是：包括在一次考验中，他们从我腿上切了块肉...

Answer 2

including one...用来修饰test
in which...用来修饰one