Gregory's Misapplied Size Constancy Scaling Explanation of the Müller-Lyer Illusion

 Gregory's misapplied size constancy scaling explanation of the Müller-Lyer illusion _____.

A) has difficulty in explaining the "dumbbell" version of the illusion
B) can easily explain three-dimensional versions of the illusion
C) is incompatible with the size-distance scaling equation
D) has been unchallenged as the only viable explanation of the illusion