Usages of yuányīn
他 不 复习 的 原因 是 太 累 了， 结果 考试 没 考好。tā bú fùxí de yuányīn shì tài lèi le, jiéguǒ kǎoshì méi kǎohǎo.
The reason he didn’t review was that he was too tired, and as a result he didn’t do well on the exam.
空气 污染 这么 严重， 一 个 原因 是 塑料 垃圾 太 多。kōngqì wūrǎn zhème yánzhòng, yì gè yuányīn shì sùliào lājī tài duō.
For air pollution to be this serious, one reason is that there is too much plastic trash.
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