The correct answer is B: when a historian is trying to understand the past by some historical figure's eyes, he/she is trying to identify which factors that person could have taken into account when deciding what to do in their time.
However, the first option (A) is also right: in order to understand what influenced a historical figure, the historian needs to know how that person thought, and felt, and understood the world around her/him.
For example: if a historian is analyzing a historical figure who was religious, he/she has to remember that that person's actions were probably influenced by his/her beliefs. Knowing someone was religious makes it necessary to understand religion as an influencing factor in that person's actions.
