C中的复合类型、常量和自动++

我正在努力理解这段代码。我一直在想为什么 d 和 e 是 int* 和 const int* . 我需要一些帮助。

const int ci = i, &cr = ci;
auto b = ci; // b is an int (top-level const in ci is dropped)
auto c = cr; // c is an int (cr is an alias for ci whose const is top-level)
auto d = &i; // d is an int*(& of an int object is int*)
auto e = &ci; // e is const int*(& of a const object is low-level const)