—Does the bookstore math books?—Yes. Do you want to______ one?
A:sell; buy
B:sell; sell
C:buy; buy
D:buy; sell
①M={ (x,y)|y=1x };
②M={(x,y)|y=sinx+1};
③M={(x,y)|y=log2x};
④M={(x,y)|y=ex﹣2}.
其中是“垂直对点集”的序号是( )