正是因为这个缘故，他才下定决心换工作。

Zhèngshì yīnwèi zhè ge yuángù, tā cái xiàdìng juéxīn huàn gōngzuò.

It is precisely because of this reason that he made up his mind to change jobs.

他今天没来上课，不知道是什么缘故。

Tā jīntiān méi lái shàngkè, bù zhīdào shì shénme yuángù.

He didn’t come to class today; I don’t know for what reason.