The 'D' paper will not respond to the context of the assignment. It does not fulfill the purpose of the essay. Most often this will mean that the essay failed to effectively react to a main idea from an essay and has no little or no support to explain the writer's reaction.
The 'C' paper will have a clear focus on reacting to the chosen essay, but may react to one of the author's subpoints rather than a main idea, or try to respond to too many ideas at once. The essay includes support that begins to explain the writer's reaction, but this support needs more detail or explanation in order to help the reader understand that reaction.
The 'B' paper will fulfill all of the criteria for the 'C' paper, and will also: have a clear focus on reacting to a specific main idea from the chosen essay. The support in this essay will be more detailed and will include connections to the overall purpose and explanations of what the evidence is supposed to prove. There still might be some areas that need more detail and/or explanation. The essay may have notable concerns with mechanics/grammar and/or proofreading that don't seriously disrupt communication, but are nonetheless distracting.
The 'A' paper will fulfill all of the criteria for the 'B' paper and will also: Have a clear focus on what is obviously a main idea from the original essay. Will include well-detailed and explained support that helps the reader understand the writer's reaction. There are no unsupported or unexplained claims made in the essay. The essay will be free from concerns with mechanics/grammar and proofreading.