shí / yàn / kāi / shǐ / qián / lǎo / shī / jiǎn / chá / le / dī / dìng / guǎn / shì / fǒu / gān / jìng

实验开始前，老师检查了滴定管是否干净。

Before the experiment began, the teacher checked whether the burette was clean.