Select the correct Passive form of the given sentence.

The prisoner is known to have assaulted the warden earlier too. 

It is known that the warden has been assaulted by the prisoner earlier too.

Answer: a; it’s a mixed format where first expression is passive and later is active. Such sentences takes ‘it’ as first subjects and the main subject is taken to the end. Present Perfect tense rule is used. ‘has/have + III Form’ is changed into ‘has/have + been + III form’