Yes. Just because your mailman reads others mail does not mean that all mailmen do the same.
The relative pronoun 'who' refers to 'people' which is a subject of this sentence, so the correct answer is C, this is also a subject.
The correct option is B.
The source of information, that would offer the most reliable fact-based information about the author is a book, that is written by the author himself. This type of source is called primary source. Information obtained from Wikipedia, movie and books published by other authors can only offer secondary information, which are not as reliable as information from primary source.
