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Visualize those little pictures as the front of vehicles like airplanes and trains. I wonder if I am right about my speculation below, and if so, if somebody could explain the exact reason. Sources are also welcome!
It seems to me that vehicle B and D have relatively less resistance against air molecules attacking them (represented by arrows) as those are the ones common in use. It also seems like A has more - and C even more - resistance against wind as they kind of point in the opposite direction of B.