Answer: A) "So goes the tale, as told by Geoffrey of Monmouth."
Explanation: an argument or claim is a statement assertion that something is true. From the given options, the one that supports the claim that the author doesn't think Geoffrey Monmouth is a reliable source about the real King Arthur, is the corresponding to option A, because it uses the word "tale" which is a fictitious or true narrative or story, especially one that is imaginatively recounted, to refer to what Geoffrey of Monmouth said about King Arthur, which shows that he doesn't believe that everything Geoffrey said was true.