1) The document discusses making subordinate sentences passive by changing the structure of sentences with a main clause and subordinate clause.
2) It provides an example of changing the sentence "People think that Jill is a very intelligent person" into the passive form "Jill is thought to be a very intelligent person by people".
3) It notes that a phenomenon to avoid is using a personal pronoun that refers to something mentioned later, like the example given of changing "Tom's sister believe that he is very generous" into the passive correct form of "Tom is believed to be very generous by his sister".