The correct answer is “analyzing historical sources and evidence.”
The historical thinking skill that the historian is using its research is “analyzing historical sources and evidence.
This technique helps the historian to analyze primary and secondary sources. The historian selects, describes, and evaluates primary resources such as the diaries written by soldiers that participated in the battle. This primary source is very important and legit as part of its research. The historian can also make connections when the film material and the photographs taken at that time in order to make its conclusions.