He knew exactly why Austin had switched sides.是什么意思？

He knew exactly why Austin had switched sides.

他完全明白奥斯汀突然倒戈转向的奥秘.

he

pron. 他，它，一个人；n. 雄性动物；

例句
Logic had prevailed and he had abandoned the idea.
最终理智占了上风，他打消了那个念头。

knew

v. 知道（ know的过去式 ），了解；

例句
She knew who to ask about finding an abortionist.
她知道向谁去打听找一个为人堕胎的。

exactly

adv. 精确地，确切地，完全地，全然，恰恰；

例句
'So it's not a family show then?' —'Well, actually, I think that's exactly what it is.'
“那么这并不是一次家庭才艺表演了？”——“嗯，事实上我觉得这恰恰就是一次家庭才艺表演。”

why

adv. （用于问句）为什么，为何，（反问，表示不必）何必，（说明理由）为什么；int. 呵唷，哎呀，嗨；n. 理由，原因，说明，难解的问题；

例句
Most people have very little difficulty in seeing why a Van Gogh is a work of genius.
多数人不难理解为什么凡·高的作品是天才之作。

Austin

n. 英国制汽车牌名；

例句
Follow Austin Creek for a few miles.
沿着奥斯汀河走上几英里。

had

v. 有（ have的过去式和过去分词 ），（亲属关系中）接受，拿，买到；

例句
He claimed that his parents had abandoned him...
他声称父母遗弃了他。

switched

v. 转变，改变( switch的过去式和过去分词 )，转换，挥动（棍棒、鞭子等），迅速转动；

例句
The workforce have recently been calling for their working hours to be reduced. Many companies have accordingly switched to a five-day week.
工人们最近一直在呼吁缩短工作时间。许多公司于是转成了一周五天工作制。

sides

n. 侧，面( side的名词复数 )，方面，侧面，一面；

例句
The warring sides have agreed on an unconditional ceasefire...
交战各方已经同意无条件休战。