GMAT Critical Reasoning (CR) | Re: Dear Editor: I feel obliged to comment on the unfair review you publis

Dear Editor: I feel obliged to comment on the unfair review you published last week written by Robert Duxbury. Your readers should know that Mr. Duxbury recently published his own book that covered the same topic as my book, which you asked him to review. It is regrettable that Mr. Duxbury should feel the need to belittle a competing work in the hope of elevating his own book.
The author of the letter above makes her point by employing which method of argument?

A) Attacking the motives of the