下列叙述正确的是( )
A．在氧化还原反应中，肯定有一种元素被氧化，另一种元素被还原
B．元素由化合态变成游离态时，它可能被氧化，也可能被还原
C．元素的原子得失电子后，一定形成8电子的稳定结构
D．有单质参加或生成的反应一定属于氧化还原反应
答案：B
在歧化反应(如Cl2＋2NaOH=NaCl＋NaClO＋H2O)中，同一种元素既被氧化，又被还原，A项错；H原子得电子后形成2电子稳定结构，C项错误；同素异形体之间的转化反应属于非氧化还原反应，D项错。
| 完形填空。 In the last 500 years, several million people have been killed by earthquakes. Among all the earthquakes, the 1976 Tangshan Earthquake is regarded as the 1 one in the twentieth century. On July 28, 1976, a terrible earthquake of 7.8 magnitude (级) 2 Tangshan City, Hebei Province. In just one second, the city with one million people was destroyed. The earthquake was __3 strong that even Beijing and Tianjin were seriously affected (受到影响). The shock was felt in 14 provinces and cities-one-third of the country. The earthquake took place 4 midnight. Most people could not take any actions.  Over 240,000 people 5 and about 170,000 were seriously injured. Water supplies, communications and traffic were completely cut off. The people there needed 6 immediately. But they could not wait for help 7 . They formed groups to dig for others. They set up medical areas and tents. They searched for food and clean water. Recovery(恢复)was not easy with so much 8 . Yet, after a lot of care was given in time, the rebuilding of Tangshan began almost 9 . Though it took time, the whole city was rebuilt and is 10 home for over a million people, earning (赢得)Tangshan the name "Brave City of China". | ||||
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