Answer:
A. A classmate also doing research on 9/11.
Step-by-step explanation:
A is correct because someone who is also doing research about 9/11 does not know much, if anything about the it. Therefore, they cannot be a credible source. B is incorrect because, while they weren't necessarily there themself, a historian has done extensive research about the event. It's their job to do research and find out whatever they can about the event. They would be a secondary source expert on the event. C is incorrect because someone who was saved was at the event, saw what happened, and their story can be backed up with facts gathered. This makes them an expert and one of the best people to talk to, considering they were there when the event happened. D is incorrect because a fireman who worked in New York that day would most likely have been called to the scene and would have seen what happened. Therefore, they are a primary, and credible source.
Hope this helps! :)