单项选择题
A.q↑.llink:=p;q+.rlink:=p↑.rlink;p↑.rlink↑.llink:=q;p↑.rlink:=q;
B.q↑.rlink:=p;q+.llink:=p↑.llink;p↑.llink↑.rlink:=q;p↑.llink:=q;
C.p↑.rlink↑.llink:=q;p↑.rlink:=q;q↑.llink:=p;q↑.rlink:=p↑.rlink;
D.p↑.11ink↑.rlink:=q;p↑.1link:=q;q↑.rlink:=p;q↑.llink:=p↑.llink;