shí / yàn / kāi / shǐ / qián / xué / shēng / xiān / jiǎn / chá / rán / shāo / chí / shì / fǒu / gān / jìng

实验开始前，学生先检查燃烧匙是否干净。

Before the experiment began, the student first checked whether the combustion spoon was clean.