Answer: Choice D
...he that was strongest secured the best place; and few left the trough satisfied
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Step-by-step explanation:
Frederick Douglass is describing the horrific conditions of what kind of food he ate and the conditions in which he had his meals. At the start of the paragraph, he describes the food itself (a corn meal called Mush). Then later on he describes how the food was served in a very degrading inhumane way (the food being served in a trough; effectively treating them as animals). Shortly after, he goes over how the food was eaten through a variety of means: use of oyster shells, shingles, or bare hands. None of which involves the regular utensils you'd expect such as a spoon.
At the very end of the excerpt, Frederick Douglass mentions that "He that ate the fastest got most; he was strongest secured the best place; and few left the trough satisfied". This effectively means that even though the food itself was horrible, and the conditions degrading, people were still hungry and had no other choice. Also, even the people who were able to eat the most weren't truly/fully fed.
So in short, the last part of the excerpt describes that the slaves weren't fed enough. If we could narrow down the cited evidence as much as possible, the portion that mentions "few left the trough satisfied" is the thing you should focus on.