我想请教两道比较疑惑的题目

我遇到两道语法题目比较疑惑.请各位指教小妹.

The nation's three military academies have seen a dramatic rise in applications, one fueld by a resurgence of patrotism, increasing tuition costs at private colleges, and improved recruiting by the academies.

答案就是A,我想问A里面为什么要使用ONE,作用是什么?

ONE 指 a dramatic rise。作用是避免歧义，不至于误认为"fueled..."修饰applications或academies。

Just as plant species native to regions with browsing mammals evolved many natural anti-browser defenses (such as sharp spines and toxic chemicals), so humans in malarial regions have evolved dozens of chemical defenses against malaria.

这道题目的答案也是A,我想问的是,为什么要使用SO,SO 的作用是什么?

(just) as ... so ... 是固定用法，用于比较相似的两个人或物。