Answer:
The correct answer is alternative D: "To evaluate the perspective of a witness to the event."
A Primary Source of information in this case would be documents, journals, articles, recording, manuscripts or other similar things that were created at the time of the events being analyzed, whereas a Secondary Source is about the same subject, but not from a source of the time of the events.
For this reason, researchers would use a primary source instead of secondary source in order to evaluate the perspective of a witness to the event, or at least of someone who lived at the time the events occurred.