A.p=head->next;head->next=head->next->next;delete p; B.head->next=head->next->next;p=head->next;delete p; C.p=head;head=head->next;delete p; D.head=head->next;p=head;delete p;
A.q=p;delete p; B.p=q;delete q; C.q->next=p->next;delete p; D.p->next=q->next;delete q;
A.s->next=head;head=s; B.s->next=head->next;head->next=s; C.head=s;s->next=head; D.head->next=s;s->next=head->next;