Final answer:
Zora’s grandmother finds her brazenness unthinkable because, during their era, African Americans faced severe punishment, like lynching, for minor offenses against racial norms, aligning with option C.
Step-by-step explanation:
In the selection from Dust Tracks on a Road, Zora’s grandmother likely finds Zora’s brazenness “unthinkable” because of the historical context in which they live. During the time the autobiography is set, which is post-Civil War America, there was a deep-seated racism that affected the African American community. Zora’s forthright behavior and disregard for societal expectations might have seemed dangerous to her grandmother, who understood the potential consequences of such behavior, including lynching or severe punishment for minor offenses against the racial norms of the time. This rationale aligns with option C, as it reflects the grandmother’s concern for the dangerous repercussions Zora's behavior could incur due to the societal racial tensions.