Hm… D looks right for single-column layout. But that might look a bit silly when it’s multi-column.
For that reason, if this alignment extends to both single- and multi-column, I choose B or C.
Actually, B might even work better for coherence when items are being shifted around when going multi-column.
Edit: It looks like they’re going with D? https://developer.blender.org/T54951
we think the best overall solution is D: Left aligned checkboxes.
“Left aligned checkboxes” for D? Am I the only one who’s confused?