It may not exactly be a primary source because it's not exactly like, for example, research paper. Research paper has been reviewed by many peers and has been tested to see if it's all true, so you can put more reliability on it.
A blog is just put up on the Internet without peer review or anything. It's raw and nobody knows what's true and what's not.
D is a false statement <span />
Well you answered the question yourself, but yes, B is the correct answer here.
