Answer:
B). "The mural was painted last year."
Step-by-step explanation:
A sentence written in passive voice pays emphasis on the object instead of the subject as the former replaces the latter in such sentences. In passive voice, the subject is being acted upon by the object and verb in the sentence(contrary to passive that involves the subject performing the action).
As per the question, option B displays the revision of the second sentence that converts it from active to passive voice as the object 'The mural' replaces the subject and the subject becomes the recipient of the action. The object is being emphasized in the revised sentence that replaces the emphasis of the original sentence(that was on subject 'some artist'). Thus, option B is the correct answer.