1 sentence

1. 数学老师强调，真子集才是原集合真的子集。

   shù​xué lǎo​shī qiáng​diào, zhēn​zǐ​jí cái shì yuán jí​hé zhēn​de zǐ​jí.

   The math teacher emphasized that a proper subset is a true subset of the original set.

   Source: Dong Chinese Dictionary