This is a good one. Looks like from GMATprep, therefore before I saw the OA, I wanted to get it right. When I read it initially, I got a little confused - it required knowledge of wheat, husking, kernel. When faced with confusion, I use diagramming technique, to understand exactly what each sentence is telling me:
1. Yeast was accidentally added to bread, though it never leavened it.
2. Leavened bread was discovered in 3000 B.C.
3. At the same time, a wheat variety whose kernel could be removed without toasting was found.
IMPLIES - This new variety helped produce leavened bread. So, something in the toasting process, or lack of it helped the process of leavening.
(C) - Heating destroys gluten necessary for leavening - this causally relates leavening and the new wheat variety.
None of the other options create any causal link. Hope this helps.