1. We include "by" and the agent when this provides necessary information: "Hamlet" was written by Shakespeare. The henhouse has been destroyed by foxes. 2. We don't include it when this information is unimportant, irrelevant or unknown: The theatre was built in 1820. ( It's the date which is important - we're not interested in the people who built it). My wallet has been stolen. ( We don't know who stole it. The relevant information is that it's missing.)

Hi Mint. i recommend you this site https://www.ego4u.com/en/cram-up/grammar/passive , it's good for english grammar/tests/vocabulary/writing and other things

Hi Mint! The passive voice is a bit tricky. Generally we wouldn't use it in conversational speech but it is useful to know about it. WE swap the object and subject, so that the 'blame' can disappear: Teacher Zowee dropped a pen becomes The pen was dropped by Teacher Zowee OR The pen was dropped. Who did it? I don't know! It's often used in news so as to remain 'objective' and not lay blame if facts haven't been proven. Have a look at this page https://www.ef.co.uk/english-resources/english-grammar/passive-voice/ or google 'esl passive voice'. Good Luck! and don't worry! thanks, Teach Zowee