设a∈R，若（a﹣i）²i（i为虚数单位）为正实数，则a=（　　）

根据已知物质和未知物质的特性，运用实验的方法，通过对比可以鉴别物质的种类。现有5瓶失去标签的溶液，分别为 HCl、H₂SO₄、BaCl₂、NaOH、CuSO₄，某同学设计了如下方案：

则步骤②选用的试剂为____；若加入的试剂③为Ba(NO₃)₂，则观察到____现象的为H₂SO₄。

按要求改写下面的句子。

    Mrs．Marks bought a printer yesterday．She was h____ because she could print anything she wanted at any time．H____,after about an hour, she was angry because she couldn't print the color blue．All the other c____ printed free, except(除了)blue，which was very unusual．

    She d____ to call the after-sales service department(售后服务部)to help her solve the problem．David answered the phone．He t____ everything he could think of to help Mrs．Marks．He asked her to reinstall(重新安装) the program，to reboot (重新启动)the computer and to turn the printer on and off．N____ of these things helped．

After hours of trying，the problem s____wasn't solved．Finally, David asked Mrs．Marks if he could go to her h____and try to solve the problem in  person．Mrs．Marks agreed and t____ him her address(住址)．When he arrived at her house，she showed him her computer and the printer. David u____what the problem was right away．He told her,“From now on，print on white paper instead of blue!”

学习了《“三颗纽扣”的房子》这篇课文,你如何看待三颗纽扣和国王?你觉得他们是怎样的人?他们在以后的日子里又发生了什么事?……把你的想法写成一篇习作来告诉我们吧!350字左右。