2 sentences

1. 古人认为，当下级发现上级有错时，应当直言规谏。

   gǔ​rén rèn​wéi, dāng xià​jí fā​xiàn shàng​jí yǒu cuò shí, yīng​dāng zhí​yán guī jiàn.

   Ancient people believed that when a subordinate finds a superior to be in error, they should offer direct admonition.

   Source: Dong Chinese Dictionary

2. 谏先生是一位非常严谨且受人尊敬的历史学教授。

   Jiàn xiān​sheng shì yī wèi fēi​cháng yán​jǐn qiě shòu rén zūn​jìng de lì​shǐ​xué jiào​shòu.

   Mr. Jian is a very rigorous and respected professor of history.

   Source: Dong Chinese Dictionary