Hi, my suggestion is that 被 cannot be used in every situations that has passive meaning. In Chinese, 被 is usually used to describe negative results, or results that you don't desire. For example, 小王的自行车被偷了。他被他爸爸打了一顿。我的咖啡被他喝光了。 事-解决；书-还给张经理；会议-举行 are quite neutral, not negative at all. So we'd avoid using 被 here. Alternatively, you may say: 这件事儿解决了 我同事把书还给了张经理 李先生 主持(host) 了今天的会议。 举行 is for large events, like annual meeting, sport games, election, etc.

Hi, 被 structure should look like: Patient + 被 + Agent + Compliment (補語) so 1. should be corrected as 这件事儿(Patient) 被 解決了(C) 。 Instead of Someone was solved by the thing. 2. should be corrected as 幾本書 (P) 被 我的同事(A) 還給了张经理。 Instead of the other way around, my college was returned by a few books to Manager Chang. 3. should be corrected as 今天的會議 (P) 被 李先生(A) 舉行/召開。 Instead of Mr. Lee was held by today's meeting. For the corrected second and third sentences, though they are grammatically correct, we tend to use 被 in negative situation. For example, he was hit by a car; the kid was scolded by her mom. Unlike in English, we don't use 被 a lot in a positive situation. For example, we don't really say he was praised by his teacher (not commonly seen in Chinese). So the second and the third sentence can be expressed in another way in Chinese, not using 被 structure: 2. 我的同事把幾本書還給了張經理。(My college returned a few books to Manager Chang.) 3. 李先生舉行了/召開了今天的會議。(Mr. Lee held today's meeting.) You can also refer to this link: https://resources.allsetlearning.com/chinese/grammar/Using_%22bei%22_sentences

Hmm. The first one should be 这件事被解决了。2nd one is 书被同事还给了张经理。and the third one you dont really ise 被 though but if you really really want to use thr grammer here it would be 会议被张经理召开了。(sound very unnatual though) hope it helps!