What Evidence Supports the Notion That,in Mental Rotation Tasks,subjects Rotate

What evidence supports the notion that,in mental rotation tasks,subjects rotate one object until it is congruent with the other?

A) Subjects are much faster when they rotate simple letters than when they rotate complex figures.
B) There is little difference between rotating objects in the picture plane versus the depth plane.
C) Subjects find it hard to recognize that one object is larger than the other.
D) Judgment time is a linear function of the number of degrees of rotation required to complete the rotation.