In one of the most stunning reversals in the history of marketing, the Coca-Cola Company in July 1985 yielded to thousands of irate consumers demanding that it should bring back the original Coke formula.
In my view, in choice D, "who" clearly refers that the consumer did the action of "demand"; but in choice b you need to take some time to think who did the action of "demand", the coca-cola company or the consumer.This is the main difference between two choices.