Read the excerpt from Roll of Thunder, Hear My Cry.

“Now, there ain't no sense in going around being mad. You clear your head so you can think sensibly. Then I want you to think real hard on whether or not Lillian Jean's worth taking a stand about, but keep in mind that Lillian Jean probably won't be the last white person to treat you this way." He turned toward me so that he looked me full in the face, and the seriousness of his eyes startled me. He held my chin up with the wide flat of his hard hand. "This here's an important decision, Cassie, very important—I want you to understand that—but I think you can handle it.”

What does the excerpt show about the historical time period of the story?

It shows that African Americans in the South experienced unjust treatment by white people that was dangerous to confront.
It shows that African Americans and white people in the South faced similar types of difficult decisions in order to survive.
It shows that African Americans in the South maintained the same level of community respect and power as their white neighbors.
It shows that African Americans and white people in the South worked together to solve disagreements that took place between families.

To answer this question, researchers studied populations of the dusky salamander (desmognathus ochrophaeus) living on different mountain ranges in the southern appalachian mountains. the researchers tested the reproductive isolation of pairs of salamander populations by leaving one male and one female together and later checking the females for the presence of sperm. four mating combinations were tested for each pair of populations (a and b)—two within the same population (female a with male a and female b with male b) and two between populations (female a with male b and female b with male a). the proportion of successful matings for each mating combination was measured. for example, when all the matings of a particular combination were successful, the researchers gave it a value of 1; when none of the matings were successful, they gave it a value of 0. then the researchers calculated an index of reproductive isolation that ranged from 0 (no isolation) to 2 (full isolation). the reproductive isolation value for two populations is the sum of the proportion of successful matings of each type within populations (aa + bb) minus the sum of the proportion of successful matings of each type between populations (ab + ba). the table provides data for the geographic distances and reproductive isolation values for 27 pairs of dusky salamander populations.