B, C, and D...I usually figure they are either pissed at me, or they are just over-correcting.
My mother tells me that when she passes cyclists on single lane roads she does so as quickly as possible when the oncoming lane is clear, so that she and they are at risk for the shortest amount of time...this does mean that she has to get back into her lane quickly as well, though, so she may understandably over-correct