A historian wants to learn more about a World War II battle. He studies diaries written by soldiers who participated in the battle, film taken during the battle itself, and photographs of the area before and after the battle. He uses the information from these sources to reach a conclusion that wouldn't have been possible by analyzing only one of them. Which historical thinking skill is the historian using?
A. Expressing a point of view
B. Evaluating bias
C. Determining context
D. Synthesizing evidence