To cast down your bucket where you are means that you don't need to travel far in order to find what you are looking for - there are many valuable resources exactly where you are.
What Washington is trying to say here is that he wants both black and white people to work together and rebuild the South in order to make it prosperous and forget about their differences.
When you answer summary questions, give a quote from the text/reading and explain it in an additional sentence.
The answer would be A. because the story is not about the glass of milk.
