Answer:
D. Negroes were not allowed to vote in the United States.
Step-by-step explanation:
Looking at the other answer choices, this is the only one that actually makes sense.
It isn't important that people may or may not have felt hot on that day, and it definitely isn't a conclusion (almost like a main idea) of the excerpt.
Also, after reading Dr. King's speech, a conclusion/important fact wouldn't be when the speech was delivered either.
Lastly, Dr. King's whole speech is against the violence that is occurring to the Negroes in their community, meaning he didn't want violence.