Final answer:
The correct passive voice conversion of 'They have already discussed the exam' is 'The exam has already been discussed by them,' as it follows the rules for constructing passive voice sentences.
Step-by-step explanation:
The active voice sentence 'They have already discussed the exam' can be changed to passive voice by following a few steps that ensure the subject of the sentence receives the action. In a passive voice, a form of the verb 'be' is used with the past participle of the main verb and includes, or implies, the preposition 'by.' We can also compare the active voice, where the subject performs the action of the verb, with the passive voice, where the subject is acted upon. Considering these rules, the correct answer is: A. The exam has already been discussed by them. This sentence correctly shifts the focus from the doers ('they') to the subject being acted upon ('the exam'), uses the appropriate 'been' form of the verb 'be,' and the past participle 'discussed.' In addition, the 'by them' part maintains the original meaning of who conducted the discussion.