If Matter Is Atomic, Then We Can Observe Only Modes

Multiple Choice

If matter is atomic, then we can observe only modes. If we do not know of the world by pure reason, then, again, we can observe only modes. Either matter is atomic or we do not know of the world by pure reason. So, we can observe only modes.
-Working backward from the conclusion of this argument, which of the following is the most likely justification of the last step of the derivation?

A) MT
B) HS
C) Impl
D) DS
E) Taut