//   按英语成绩排序
struct stu  *sort_english(struct stu  *head)   
{
    struct stu  *p;
    struct stu  *p1;
    struct stu  *p2;
    struct stu  *p3;
    struct stu  h;
    struct stu  t;
    if (head == NULL)
    {
        return NULL;
    }
    h.next=head;
    p=&h;
    while (p->next!=NULL)
    {
        p=p->next;
    }
    p=p->next=&t;
    while (p!=h.next)
    {
        p3=&h;
        p1=p3->next;
        p2=p1->next;
        while (p2!=p)
        {
            if ((p1->s[2] )<(p2->s[2]))
            {
                p1->next=p2->next;
                p2->next=p1;
                p3->next=p2;
                p3=p2;
                p2=p1->next;
            }
           else
            {
                p3=p1;
                p1=p2;
                p2=p2->next;
            }
        }
        p=p1;
    }
    while (p->next!=&t)
    {
        p=p->next;
        }
    p->next=NULL;
    return h.next;
}