For retraction of maxillary anteriors by 1 mm, space required is?: (A) 1 mm, (B) 2 mm, (C) 0.5 mm, (D) 1.5 mm
Answer is B. For every 1 mm of decrowding, same amount required for alignment. 
For every 1 mm of leveling the curve of spee, 0.5 mm space required in the arch. 
For every 1 mm of incisor retraction, 2 mm space required.