Which example best illustrates a round character?

A round character is one that is well-developed and has a complex personality, often displaying a range of emotions and traits that evolve throughout the narrative. This character typically undergoes significant development or change as they encounter various experiences, allowing readers to gain a deeper understanding of their motivations, relationships, and inner conflicts.

In contrast to round characters, characters that remain static or change little (as found in the first choice) are known as flat characters. These types lack depth and do not show the complexity that round characters possess. The option describing a character whose sole purpose is to advance the plot indicates a functional character, often a flat or stereotypical character that doesn't demonstrate much complexity or personal growth. Lastly, a character defined by one primary trait can also be seen as flat because they lack the multifaceted nature of a round character. The complexity and evolution highlighted in the chosen answer make it the most appropriate example of a round character.