It fails to present contrary evidence. It requires confirmation that the change in the professor's students is representative of a change among college students in general. It offers no proof to the effect that the professor is an accurate judge of writing ability. It does not take into account the possibility that the professor is a poor teacher.
College professor: College students do not write nearly as well as they used to. Almost all of the papers that my students have done for me this year have been poorly written and ungrammatical.
Which one of the following is the most serious weakness in the argument made by the professor?