The correct answer is D. motivation.
When analyzing a character, readers often look for clues in the character's behavior, dialogue, and decisions to understand what drives them—essentially, their motivation. A character's motivation explains why they act in certain ways and helps to unpack their intentions and desires.
While actions (A) are a part of understanding a character, they are not the end goal of the analysis; rather, they serve as a window into the character's motivations. Development (B) refers to how the character changes over time, and theme (C) is broader, related to the underlying messages or ideas in the narrative.
Motivation is the most directly tied to the inferences that readers make based on character analysis.