D - corners are in scatter-shadow.
We're already in shadow from the direct light, so the shadows you're seeing within the shadow are entirely scatter-shadows.
C - corners receive less scattered light.
Notice how the corner is darker, particularly very near to the corner.
A -Corners receive less direct light.
corners receive less scattered light.
Again, the very innermost part of the corner has quite a dark line where very little scattered light reaches.