Hi, A and D are extremely similar, but with one major difference. A tells us that the inner workings of the brain are chemical not electrical, while D tells us that specifically the way the impulses are passed from cell to cell is chemical not electrical. In this sense, D is much narrower. We don't actually know that there is no role for electricity in the inner workings of the brain as A implies, but we do know that the process described in D is chemical, not electrical.
