All of the options you provided can describe purposes of creation stories, but if we are looking for a primary purpose, it often centers around explaining how the earth and the universe came to be. However, creation stories also serve to convey cultural values, teach lessons for survival, and preserve the history and traditions of a people, including stories about ancestors and rituals.
If you need to choose one, "to illustrate how the earth came to be" is often seen as a fundamental purpose of creation stories. But recognizing the multifaceted roles they play in various cultures is important as well.