So, to show some light on this:
1. It is A if you go strictly by the T&C's
2. The reality is that you've always had until midnight of the next day in SABRE. So, in practice, it is C.
D is really stretching it. As we know with AA, ticketing can be slow and occasionally takes multiple days (I would never rely on D).
WARNING: If you go by anything other than A, you are taking a risk that you won't be able to cancel for free.