—— do I need to feed the pet dog? ——Twice a day.

一次家庭探究活动中，小明把一个正在发光的灯泡放到U形磁体中间，惊讶的发现了灯丝在晃动。关于这种现象，下列说法正确的是（　　）

Are you looking for something fun and would you like to help other people in your free time? Then join us．
We have jobs for people of all ages；Anyone from twelve-year-old children to 80-year-old people can become one of us．
You can help people in many ways．Schools need help with taking care of children while their parents are working．Hospitals need us to look after children while their parents see a doctor．Animal lovers can help take care of those dogs and cats without homes．There is something to do for everyone．
"As a member of this group，I don’t want to get anything．Seeing the children's happy faces，I am happy，too．"said Susan，an old woman of 62．  
"I often played computer games in my free time before．Now I help older people learn how to use Computers，"said another one at the age of 18．
If everyone helps out a bit， we'll all have a better world to live in．
Interested? Call us on 3847613 or visit our website(网站)：http：//www．activol．com．

地球上的物体和宇宙中的天体都是由物质组成的，物质处于不停的____ 和____ 之中；一切物质都是由____ 组成，分子是由____ 组成，原子由____ 和____组成．

河流的中下游河段侧蚀作用明显,河流不断地侵蚀河岸、扩展河床,致使河道不断弯曲,以致河道变迁。读某河段曲流分布示意图,回答下列各题。