After-School Activities Running Late Entails That the Buses Will Run

Multiple Choice

After-school activities running late entails that the buses will run late. The buses running late is a sufficient condition for either Carlos and Deandra getting home late or Edna missing dinner. Either after-school activities run late but Carlos doesn't get home late, or after-school activities run late but Deandra doesn't get home late. So, Edna misses dinner.
-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) MP
B) Simp
C) DN
D) DS
E) HS