A、p↑.rlink↑.llink:=q;p↑.rlink:=q;q↑.llink:=p;q↑.rlink:=p↑.rlink;
B、p↑.llink↑.rlink:=q;p↑.llink:=q;q↑.rlink:=p;q↑.llink:=p↑.llink;
C、q↑.llink:=p;q↑.rlink:=p↑.rlink;p↑.rlink↑.llink:=q;p↑.rlink:=q;
D、q↑.rlind:=p;q↑.llink:=p↑.llink;p↑.llink↑.rlink:=q;p↑.llink:=q;
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