A.
We need two functions handling different cases (when n is even or odd). 问题需要按照“n为奇数”、“n为偶数”两种情况分别设计两个函数
B.
The sequence of recursive callls is terminated when the problem size is reduced to either 0 or 1. 在问题规模缩减为0或1时,停止递归
C.
The program returns to the main function when the problem size is reduced to either 0 or 1. 在问题规模缩减为0或1时,返回main函数(或递归函数被调用的函数)
D.
Two sub-instances are generated from every instance of the recursive calls. 递归函数在执行过每次创建两个递归实例