@hallerae the flaw here is that the professor is overgeneralizing from his students to college students in general.
Notice his conclusion is, "College students do not write nearly as well as they used to," but the support he provides for this is "almost all of the papers that my students have done for me this year . . . "
The problem with (B) is that a college professor would be an accurate judge of writing ability, particularly a college professor in a class that requires the submission of papers.
Hope that helps! Please let us know if you have any other questions.
