Why does Hosseini divide the book into four sections?

He splits the book into four sections in order to concentrate on character development.

"Hosseini divides the book into four sections. The first two introduce us to his two female characters separately. The third joins their storylines, and the fourth shows us what rises after all the dust. And, in the first section, Hosseini proves himself a keen user of natural symbols and of nature in general, even the limited nature of Afghanistan's rugged terrain. He brilliantly in chapters five and chapter 13 uses the idea of a "gust of wind" to represent motherhood, at one point the end of motherhood, and in the latter the beginning of it."

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