1) S. + P.+ O.?

O. clause >>>> it?

They know that he is an expert. >>>> It is known that he is an expert.

2) S. + P. + Ind. O. + Dir. O.

? ? He told her a long story. >>>> She was told a long story. >>>> A long story was told to her.

3) S. + P. + O. + O. C.

? ? They chose Tom captain. >>>> Tom was chosen captain.

In below situation, ACTIVE VOICE cannot be changed to PASSIVE VOICE

1) when predicate is LEAVE, ENTER, REACH, RESEMBLE, BECOME, SUIT, BENEFIT, LACK

2) when predicate is the unbreakable verb phrase such as TAKE PLACE, LOSE HEART, CHANGE COLOR, BELONG TO, CONSIST OF

3) when object is reflexive pronoun,?reciprocal pronoun (each other, one another), infinitive, gerund

4) when object is it?