Question

the reason a character thinks, feels, or acts a specific way is called
thematic development.
plot structure.
character motivation.
prior knowledge.

Explanation:

The term refers to the reason behind a character's thoughts, feelings, or actions, which matches the definition of character motivation. Thematic development relates to theme progression, plot structure is the arrangement of story events, and prior knowledge is existing information—none of these fit the described concept.

Answer:

character motivation.