(C) is incorrect because Millie is not contesting the fact that Oscar had received Myer's permission to quote his work without attribution, but rather saying that even if Oscar had permission from the author it is still plagiarism because it misleads the readers even if the original author is fine with it. Millie and Oscar essentially have different perspectives on what constitutes plagiarism. Oscar argues that as long as he got author's permission it is not plagiarism. Millie responds by saying that plagiarism is not only about protecting the author's rights but also the reader's, hence any quote without attribution is still plagiarism whether one has the permission of the author or not.
