题目

Disasters happen all the time somewhere in the world. Are you ready if one hits your neighborhood next week? Find out what you need to do now before it is too late. Let’s take an earthquake for example. During an earthquake, get under a strong object like the kitchen table. Don’t leave the building during the shaking, or you might be hurt by falling objects from the outside of the building. When you are in bed during the night and an earthquake happens，simply roll off the bed. There will be a safe void around the bed. If you are watching TV and you cannot easily run away by getting out t下列化学符号中的数字“2”表示的意义不正确的是（ ）A. 2Zn：“2”表示两个锌元素B. 2OH﹣：“2”表示两个氢氧根离子C. NO2：“2”表示一个二氧化氮分子含有两个氧原子D. ：“+2”表示氧化镁中镁元素的化合价为+2价