单项选择题

A.q:=p↑.link;p↑.link:=q↑.link;
B.p↑.link:=q↑.link;q:=p↑.link;
C.q↑.link:=p↑.link;p↑.link:=q;
D.p↑.link:=q;q↑.link:=p↑.link;