①S₁+S₂=S₃+S₄；②S₂+S₄=S₁+S₃；③若S₃=2S₁，则S₄=2S₂；④若S₁=S₂，则P点在矩形的对角线上．

其中正确的结论的序号是____（把所有正确结论的序号都填在横线上）．

注意：1). 词数80左右（短文的开头结尾已给出，不计入总词数）；

          2). 不得透露学校、姓名等任何个人信息，否则不予评分。

Dear Sandy,

     Welcome to my hometown!  

                                                                                                                                                                                             Yours,

                                                                                                                                                                                               Li Lei

背着小蛛的七个月里，母蛛要随时喂它们吃东西。