问题
选择题
It was not until yesterday ______ he returned _______ to know the news. [ ]
A. that ; that I got
B. when ; that did I get
C. when ; that I got
D. that ; that did I get
答案
答案：C
搜题请搜索小程序“爱下问搜题”
It was not until yesterday ______ he returned _______ to know the news. [ ]
A. that ; that I got
B. when ; that did I get
C. when ; that I got
D. that ; that did I get
答案：C
某同学从定量角度研究过氧化氢溶液制取氧气的过程，对原实验进行部分改进，增加了称量操作．具体做法是：取溶质质量分数为10%的过氧化氢溶液和少量的二氧化锰放入气体发生装置，并对反应前后混合物的质量进行称量，记录如下：
| 反应过程 | 反应前 | 反应后 |
| 质量变化（不含容器质量） | 34.3g | 32.7g |
（1）制得氧气的质量为______克．
（2）请你列式计算所取过氧化氢溶液的质量为多少克？