diào / chá / jié / guǒ / yǐ / jīng / xiǎn / míng / shì / gù / zhǔ / yào / shì / yóu / cāo / zuò / shī / wù / zào / chéng / de

调查结果已经显明，事故主要是由操作失误造成的。

The investigation results have made it clear that the accident was mainly caused by operational errors.