Final answer:
Mary Warren is the flat character in 'The Crucible'.The correct option is D.
Step-by-step explanation:
In Arthur Miller's play The Crucible, a flat character is one who does not undergo significant change or development throughout the story. In this case, the flat character is Mary Warren, one of the girls involved in the witchcraft trials. Mary Warren remains largely unchanged and does not experience much growth or transformation, unlike other characters such as John Proctor, Abigail Williams, and Reverend Hale who undergo significant development and change throughout the play. Therefore, the correct answer is d) Mary Warren.