Which of the following rules is not correct (with reference to voice change)?
1
During changing a sentence from active voice to passive voice, the object and subject are interchanged with each other, i.e. object of the active sentence become the subject of the passive sentence and vice versa.
2
The verb in the active sentence is changed into the past participle form in the passive sentence
3
The subject usually comes at the end, preceded by the preposition 'by'.
4
During conversion, the case of the subject in active voice is not changed in passive.