A. Jan, the doctor is correct concerning punctuation. Hello,I have some questions in relation to passive. Farmers spray the trees each week. The agent doesn't have to be at the end of the Verb Phrase. This is not actually what is happening in the sentences below, however.
Farmers spray the trees each week.
As for the remaining sentences, all of them are grammatical. However, I have no way of explaining why in a simple straight-forward way. Rather, it's a question about the status of PPs that modify nouns. In English, it is possible to passivize the basic NP and leave the PPs that modify it behind. The maids were cleaning the rooms in the hotel when we arrived.