为了防止病虫害，农民常会对生长过程中的蔬菜喷洒农药．据有关专家介绍，用清水，特别是碱性溶液浸泡冲洗蔬菜，可使残留在蔬菜上的农药毒性降低．因此买来的蔬菜在食用前可用清水浸泡一段时间，浸泡蔬菜时最好加入适量下列物质中的（　　）

写作。

     题目：痕迹
     要求：①写一篇600字左右的文章；②不得透露个人相关信息，不得抄袭。

①空气 ②氯酸钾 ③氧气 ④澄清石灰水 ⑤矿泉水 等物质中，（填序号）

属于混合物的是____属于纯净物的是____．

      There are  1 days  2 a week. They are  3 , Tuesday, Wednesday, Thursday, Friday, Saturday and4  .Sunday is the first day 5 a week. Monday is the second day of a week. The last day of a week is Saturday.  6  China, people work 7days a week. They go to work from Monday 8  Friday. They don't go to work 9 Saturdays and Sundays . They stay 10  home.

若a，b互为相反数，c，d互为倒数，|m|=2，求$\frac{a+b}{4m}$+m²﹣3cd的值．