Dear student,
Here are the answers:
1) The tree was cut down by the man.
Explanation:
1) The object of the sentence becomes the subject in passive voice.
2) Use the past participle of the main verb in passive voice.
3) The word "by" is used sometimes in passive voice.
2) He was arrested.
Explanation:
1) The object of the sentence becomes the subject in passive voice.
2) Use the past participle of the main verb in passive voice.
3) The pronoun "him" changes to "he".
3) The word "by" is not always used in passive voice. Here we would not use "by the police" because we know that the policemen only arrest people.
Regards