A Positive Lens Has a Focal Length F

Multiple Choice

A positive lens has a focal length f.The only way to get a magnification of -1 is to

A) place a real object at the focal point.
B) place a real object at a distance 2f from the lens.
C) place a virtual object at a distance 2f from the lens.
D) Magnifications can never be negative.
E) None of these is correct.