Answer: A. at the point which
is twice the focal lenght of the lens of the camera
Explanation:
When a certain document is to be produced through the use of a duplicating camera, it should be noted that the camera should be placed at the point which is twice the focal lenght of the lens of the camera so as to get the exact copy of the document.
It should be noted that placing the camera between the principal and a point twice the focal lens of the camera lens or beyond a point that's twice the focal length will not produce the document.
Therefore, the correct option is A