2 sentences

1. 反切是中国古代的一种注音方法。

   fǎn qiè shì Zhōng​guó gǔ​dài de yī zhǒng zhù​yīn fāng​fǎ.

   Fanqie is a method of indicating pronunciation used in ancient China.

   Source: Dong Chinese Dictionary

2. 在古代汉语课上，老师讲解了德字在反切中的用法。

   zài gǔ​dài Hàn​yǔ kè shàng, lǎo​shī jiǎng​jiě le dé zì zài fǎn qiè zhōng de yòng​fǎ.

   In the Ancient Chinese class, the teacher explained the use of the character '德' in fanqie.

   Source: Dong Chinese Dictionary