某无色溶液中可能含有Na⁺、K⁺、I^﹣、Cu²⁺、CO₃^2﹣、SO₄^2﹣等离子中的全部或其中的几种．现进行如下操作：

①用洁净的铂丝蘸取溶液在无色火焰上灼烧，火焰呈黄色；

②把溶液分成2份，向一份溶液中加入淀粉溶液，再通入氯气，溶液呈蓝色；

③向另一份溶液中加入过量稀硫酸后，产生无色气体，再加氯化钡溶液后，产生白色沉淀．

请填写下列空白：

种群密度的取样调查对于不同种类的生物采用的方法存在着差异．

     Tom and Mike are good friends. They are good with children. They want to find jobs in summer vacation. This Friday Tom tells Mike that Sunson School Trip needs teachers to help with sports, music and computer. Mike is glad to know that.
    Tom can play basketball, volleyball, and he can swim. Mike can play the violin, the trumpet, the drums and the guitar, and he can swim,too. Tom and Mike like computers very much. Can they join Sunson School Trip?

明清时期，统治者推行“海禁”和“闭关锁国”政策，造成的影响主要有
①保护了民族工业发展        ②妨碍了对海外市场的拓展
③避免了西方殖民侵略       ④中国逐渐落伍于世界潮流

在解决问题时，求同存异（  ）
①是父母与子女解决矛盾和问题，进行沟通的理想结果
②有利于解决争端
③有利于矛盾双方相互接受对方的观点
④有利于双方进行友好的合作