I like A, as it iterates toward C anyway. You can deliver value with the naïve implementation delivered quickly. If Mary Jones has further requirements that w

I like A, as it iterates toward C anyway. You can deliver value with the naïve implementation delivered quickly. If Mary Jones has further requirements that were not considered at the outset, now she'll be able to consider them. Conversely, if you've built a bunch of assumptions into your code, they'll be tested in the real world sooner rather than later.