向一个栈顶指针为 hs 的链式栈中插入一个指针 s 指向的结点时，应执行（ ）。

• A.hs->next = s;
• B.s->next = hs; hs = s;
• C.s->next = hs->next; hs->next = s;
• D.s->next = hs; hs = hs->next;