呐_凝凝_刚刚给你打了电话告诉你答案的说~
AB+BC>AC a+b>m
AB+AD>BD a+b>n
AO+BO>AB (m+n)/2>a m+n>2a
AO+DO>AD (m+n)/2>b m+n>2b
2a+2b>m+n>a+