An article "The Way to Rainy Mountain Themes: Memory and History" by Sylvie McNamara say this about the way the book is structured,

"Momaday’s focus on memory also emphasizes that the past must be actively transmitted in order to preserve Kiowa culture and identity. History is not an abstract time that is relegated only to the past; it is a set of stories, values, and ideas that live on through people who make the effort to remember."

Which statement accurately reflects why Momaday chose 3 voices to use as the structure for his book.

He wanted to be innovative in his structure and do something no one had done before.

He needed a way to set his writing apart from other works about Native Americans.

He didn't have enough to write about in memoir so he added other voices.

He believes that the 3 voices provide the most thorough reflection of the Kiowa history.