If you don't know if an author is credible, you should research him/ her.
The answer is not B because you should never discredit an author without valid reasoning. The answer could also not be to ignore because you could be missing the chance that the author is credible and then lose a valued piece of information. If you write an author, the author could be either dead or choose to ignore your letter. This leaves us with the answer C which is the correct answer.
