The correct answer is C) Yes, because Nicolaus interviewed many of the people there.
This a reliable source for a historian to use when writing about Caesar’s death because Nicolaus interviewed many of the people there.
Although it is not a hundred percent bulletproof reliable story, it can be considered reliable in that Damascus wrote it using testimonies of people that witnessed the incident. Let's remember that a primary source is the one that directly witnessed the event. It could be a journal, a letter, a photograph of people that were there. But secondary sources are also valid when the research is done properly and the sources are serious and double-checked.