I believe it’s C it might be wrong
1. A letter was being written by him.
2. The room had been cleaned by us.
3. He is known to me.
4. The homework has been done by me.
5. The exercise had been done by me.
Hope this helps! Remember that you are using passive voice when the subject is being acted upon by the verb.
D. The correct answer is me
Corrupt business practices, i believe
C is the correct answer. The common nouns here are: object, magazine, floor. The other sentences do not have three common nouns, therefore these are not the correct options.