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（ ）。
hs->next = s;
s->next = hs; hs = s;
s->next = hs->next; hs->next = s;
s->next = hs; hs = hs->next;
