问题
选择题
What satisfies us is that the position of the house combines quietness and ________.[ ]
A. convenience
B. efficiency
C. variety
D. settlement
答案
答案：A
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What satisfies us is that the position of the house combines quietness and ________.[ ]
A. convenience
B. efficiency
C. variety
D. settlement
答案：A
通过下表，可以总结出“在原子里质子数等于电子数”．
| 原子种类 | 氢 | 碳 | 氧 | 钠 | 铁 |
| 质子数 | 1 | 6 | 8 | 11 | 26 |
| 中子数 | 0 | 6 | 8 | 12 | 30 |
| 核外电子数 | 1 | 6 | 8 | 11 | 26 |
| 相对原子质量 | 1 | 12 | 16 | 23 | 56 |
（1）______．
（2）______．
（3）______．
（4）______．