Read this excerpt from "The World on Turtle's Back." The conflict between the twins continued, and for some reason, the grandmother favored the left-handed twin. The right-handed twin became angry and resentful. He was the truthful twin who always did the right thing. The left-handed twin was deceitful and did everything backward. You could never trust him.

The twins represented the two ways of the world which are in all people. The Indians did not call these good and evil. They called them the straight mind and the crooked mind, the righteous man and the devious man, the right and the left.

The main purpose of this excerpt is to
A. demonstrate that right-handed people are good and left-handed people are bad.
B. explain why some people do the right thing and others do not.
C. provide the reason why the grandmother favored the left-handed twin.
D. clarify what the Iroquois considered the two different sides of human nature.