问题
选择题
We would like to go and thank him yourselves, but we ________ out his address yet.[ ]
A. haven't found
B. had'n, t found
C. didn't find
D. don't find
答案
答案：A
搜题请搜索小程序“爱下问搜题”
We would like to go and thank him yourselves, but we ________ out his address yet.[ ]
A. haven't found
B. had'n, t found
C. didn't find
D. don't find
答案：A
某同学想探究二氧化锰在过氧化氢分解中作催化剂，设计了以下探究实验，请你完成实验报告和实验分析．
（1）实验报告：
| 实验步骤 | 用带火星的木条检验时的现象 | 结论 |
| 1．向试管1中倒入5mL5%的过氧化氢溶液 | 不复燃 | 几乎无氧气放出 |
| 2．给试管1稍微加热 | ① | ② |
| 3．向试管2中加入5mL5%的过氧化氢溶液和一匙二氧化锰 | ③ | ④ |
| 4．待试管2中无气泡冒出时再倒入5mL5%的过氧化氢溶液 | ⑤ | ⑥ |
| 5．再向试管2中加入一匙二氧化锰 | ⑦ | ⑧ |
①比较步骤1和步骤2可得出结论：过氧化氢溶液不加热几乎无氧气放出，稍加热有氧气放出．
②比较步骤1和步骤3可得出结论：______
③比较步骤4和步骤5可得出结论：______
（3）该同学觉得该实验还不完美．他还想证明MnO2在反应前后质量不变，你认为他该增加什么实验？