C. film set in some previous time in history.
Explanation:
The options B and Care closely associated with each other. While the answer is indeed C, as the period piece first and foremost is set in some previous time in history and not contemporary period.
But it is also to be remembered that a good historical piece is able to give a sociological picture of the time it describes with accuracy and to tell of the events it deals with in considerable historical accuracy. So the element of historicity must be preserved.
