huà / xué / kè / shàng / lǎo / shī / jiǎng / jiě / le / tóng / sù / yì / xíng / tǐ / de / xíng / chéng / yuán / yīn

化学课上，老师讲解了同素异形体的形成原因。

In chemistry class, the teacher explained how allotropes are formed.