I studied grammar books about passive voice.
However, I am not very clear about some passive voice constructures.
Could you have a look at sentences I practiced?
1Active:I heard him sing a song.
Passive voice:He was heard to sing a song.
In the active, I heard is simple-past-tensed, so in the passive He must be followed by a verb or part of the verb phrase corresponding to the same tense; hence we get He was heard... (not is heard)
2.Active:What did he buy?
Passive voice:What is bought by him?
The same rule applies here - in the active, What did he buy? is in the simple past tense; so in the passive, is bought should read was bought:
What was bought by him?
3.Active:Who will clean the dirty car?
Passive voice:By whom will the dirty car be cleaned?
You could also say:
Who will the dirty car be cleaned by?
4.Active:They think that mary can accept the new idea.
Passive voice: Mary was thought to accept the new idea.
They think is in the present simple tense; so the passivized sentence should read:
Mary is thought to (be able to) accept the new idea.
I am wondering if all my tries about passive voice are right and idiomatic.
Thanks for your check and correction.