2 sentences

1. 听讲座时，你应该保持安静。

   tīng jiǎng​zuò shí, nǐ yīng​gāi bǎo​chí ān​jìng.

   When listening to a lecture, you should be quiet.

   Source: Tatoeba

2. 他在听讲座的时候打了个瞌睡。

   tā zài tīng jiǎng​zuò de shí​hou dǎ le gè kē​shuì.

   He dozed off while listening to the lecture.

   Source: Dong Chinese Dictionary