Answer:
The details from "The Oasis: Africa" best support the central idea that nature can be severe and unkind are "For eight weary days we had crawled across the burning desert."
Explanation:
The sentence "The Oasis: Africa" best support the central idea that nature can be severe and unkind are "For eight weary days we had crawled across the burning desert." is the only one that talks about natural elements and how harmful they can be to humans, the other options talk about poverty and consequences of it.