Grammatical errors are minimal. C. is for an average paper that complies with the topic assigned or chosen. The student has done just what I asked for. Grammar is fair and content is intelligible. D. is for a paper written with a level of grammatical errors that sometimes hinders the comprehension.
Ideas exist but are arranged without a clear logic.
Some of them are obscure and unintelligible. This grade signifies an unacceptable performance in writing a specific assignment. Usually the content can hardly be grasped because of a lack of clarity and organization. When writing a paper, do not make unsupported assertions. Try to present the most convincing case for your argument.