diào / chá / rén / yuán / jué / dìng / qióng / yuán / jìng / wěi / chá / qīng / shì / gù / fā / shēng / de / zhēn / zhèng / yuán / yīn

调查人员决定穷原竟委，查清事故发生的真正原因。

The investigators decided to get to the bottom of the matter and find the true cause of the accident.