Answer:
Mary Warren was used by Proctor in the court scene to hopefully prove his innocence as a witch. However, Mary Warren is also branded as a witch by Abigail when she contrives a devilish bird in the sky that she screams was sent by Warren herself. In the Crucible, Warren doesn't really have a good track record with either side as she just ends up getting manipulated. 
Explanation:
 
        
                    
             
        
        
        
Short paragraphs, un varied punctuation, the redundant use of the subjects name
 
        
             
        
        
        
"objective; object of preposition" Is your answer.