Is back-face culling considered a technique/optimization of ray tracing?
I would exclude (A) for the following reasons:


In any modern ray-tracer, the acceleration structure (BVH, k-d tree, etc) holding your geometry is the primary source of culling. The final list of primitives to trace for a given ray may include non-visible triangles, but ideally there should be very few with good acceleration structures.
Ray tracers support many more primitives than just triangles. (How do you back-face cull a sphere?)


The following problems with back-face culling in general are also more relevant to ray tracing:


Transparent materials (such as glass) will make certain objects render incorrectly with back-face culling applied.
Non-closed meshes (like plants) need to render the back-facing triangles.