Final answer:
Brandon should choose a book written by a football historian as a secondary source for his research paper on changes in the game of football during the twentieth century.
Step-by-step explanation:
For Brandon, who is writing a research paper on the topic of changes in the game of football in the twentieth century and needs to use a secondary source, the best choice would be B. A book written by a football historian. This type of source is written after the fact and provides scholarly analysis based on primary sources. It sets context and relates the topic to its era, as well as providing insights into how historians have previously interpreted the information. Options A (an interview with a current football player) and D (a personal blog about someone's football experience) could be considered primary sources or anecdotal evidence, while C (a fictional novel) is not a factual source suitable for research.