The best indicator of a person's level of optimism is his or her

A) conscientiousness.
B) locus of control.
C) attributional style.
D) self-serving bias.

Attributional style refers to how individuals explain the causes of events or outcomes in their lives, whether they attribute them to external factors (such as luck or circumstance) or internal factors (such as their own abilities or efforts). Optimistic individuals tend to have a more positive attributional style, with a tendency to attribute positive events to internal, stable, and global factors, and negative events to external, unstable, and specific factors. This contrasts with a more negative attributional style in pessimistic individuals, who tend to do the opposite. Therefore, C is the best choice as it directly relates to optimism.