Why is B wrong?

Hi, the initial argument starts out by telling us that if something happens, then one of two outcomes will happen, bc then gives us a necessary conclusion for each of those two outcomes. In other words If E then A or B If a then x If b then z In b however, we never do anything with the second possibility, the B. It goes If w then r or n If r then s or c To match the original passage we need to do something more with N, which b does not do.