Independent news sources should be evaluated A more carefully than mainstream news sources B as closely as mainstream news sources C less thoroughly than mainstream news sources

The correct answer is B as closely as mainstream news sources.

Indeed, sources of information should be evaluated not based on their public status but on the own intrinsic merits of the information they are divulging. Mainstream sources of information may be as biased, erroneous and sensationalist as independent sources and what actually matters to determine the reliability and the accuracy of a source is its journalistic and investigative integrity and not its media status.