我国是一个气象灾害严重的国家，对我国农业生产影响最大、最常见且分布最广的一种气象灾害是（   ）

某化学兴趣小组的同学在实验室发现以前用的一瓶氢氧化钠溶液忘记了盖瓶塞，他们取这种氢氧化钠溶液少量于试管中，再逐滴加入稀盐酸，观察到有气泡产生．小组中有同学断定，这瓶氢氧化钠溶液已经变质．辅导老师肯定了该同学的看法，又有同学提出：所用氢氧化钠溶液是否完全变质？兴趣小组的同学在辅导老师的鼓励下又进行了如下的实验探究：

【提出问题】氢氧化钠溶液是否完全变质？

【进行猜想】（1）该氢氧化钠溶液部分变质；（2）该氢氧化钠溶液全部变质．

【查阅资料】氯化钡溶液呈中性．

观察下列各式：$5^5=3125$，$5^6=15625$，$5^7=78125$ ，$\cdots$，则5²⁰¹¹的末四位数字为（   ）

（2015•广东佛山）阅读下面短文，掌握其大意，然后根据短文内容和首字母提示，在短文空白处填入适当的单词，使短文内容通顺、合理。

Electricity is a type of energy that was discovered over 100 years ago. One of the most common w____  to make electricity is by changing other energy sources (来源), such as coal, and oil or solar, wind and falling water. You may not even realize that electricity is a huge part of your e____  life. Basically, it keeps your home and school w____  in winter and cool in summer. W____  it, you would never be able to watch your favourite TV show or listen to your MP3 player. Have you ever i____ a world in which you can't turn on a light, a computer, or even use the phone? So electricity is important to us and we n____  electricity. That's why it's time to rethink our relationship with this v____  resource (资源) and think about h____  we can do our part to use it wisely.