题目

Most English people have three names：a first name，a middle name and a family name．Their family names come last．For example，my full name is Jim Allan Green．Green is my family name．My parents gave me both of my other names．     People don't use their middle name very much．So“John Henry Brown”is usually called（称作）“John Brown”．People never use Mr，Mrs or Miss before their first names．So，you can say John Brown；but you should never say Mr. John．They use Mr，Mrs．Or Miss with the family name．     Sometimes people ask me about my name．“Why do 如图（1），矩形纸片ABCD，把它沿对角线BD向上折叠，（1）在图（2）中用实线画出折叠后得到的图形（要求尺规作图，保留作图痕迹，不写作法）（2）折叠后重合部分是什么图形？说明理由．