Answer:
d) The grandmother's love for one twin and hate for the other.
Explanation:
There are a few subtle variations to this narrative, but they all start with the Sky Goddess giving birth to a daughter named Tekawerahkwa on Earth. Tekawerahkwa develops feelings for West Wind, a formidable force, when she's older. It turns out that they hit it off, got hitched, and now have twins. Good and Evil are the names of the two sons.