题目

阅读下面短文，根据其内容写一篇 60 词左右的内容概要。 School uniforms are becoming more and more popular across the U.S.A. That's no surprise, because theyoffer many benefits. They immediately end the powerful social sorting and labeling (标记) that come from clothing. If all students are dressed in the same way, they will not pay too much attention to their clothing, and someof them will not be laughed atfor wearing the“wrong” clothes. Some people are against the strict rule of school uniforms, but they do not realize that students already accept a kind of rule 19．已知四边形ABCD的四边分别是a，b，c，d，且a4+b4+c4+d4=4abcd，求证：四边形ABCD是菱形．