问题 多选题

关于机械运动和参考系,下列说法中正确的是(  )

A.一个物体相对于另一个物体位置的变化,叫做机械运动

B.参考系必须是和地面连在一起的物体

C.参考系可以是运动的物体

D.任何物体都可以被选作参考系

答案

A、我们在研究物体的运动和静止情况要先选择一个假定不动的物体作为参照物,再看被研究物体相对于参照物是否有位置的变化,如果有变化,被研究物体就是运动的,如果没有变化,被研究物体就是静止的,所以一个物体相对于另一个物体位置的变化,叫做机械运动,故A正确;

B、参照物的选择,原则上是任意的,不一定要和地面联系在一起,故B错误;

C、参照物的选择,原则上是任意的,静的可以作参照物,动的也可以作参照物,故CD正确.

故选ACD.

问答题
阅读理解

One very cold day,a snowstorm blew into our area. Needing firewood,I quickly set out with my best friend,Bruce,to look for a tree to cut down. I was glad to have Bruce along with. Cutting down a tree in a snowstorm can be dangerous. So it was important to have a friend who could warn me of danger.

When I chose a big tree about 23 meters tall and prepared to cut it down,my best friend suddenly warned me,“Don’t cut down that tree!It’s too close to the power line!﹙电线﹚”I wasn’t sure about it. So I decided to disregard his warning. I wanted to finish the job quickly and go home. So I began cutting down the tree. When the tree fell,there was no longer any doubt that my friend was right.

The tree caught the power line,bringing it to the ground. I considered cutting the tree off the line. After all,electricity can’t travel through wood,so I could safely remove the tree. As I reached out my finger to touch the tree,pain ran up my arm and through my head. I was shocked!

After I returned home and told my mother what had happened,she quickly called the power company. The workers from the power company soon arrived on the scene. One of them asked if I had touched the tree,and when I told him I had,his face turned pale.

“You should have been killed,” he said.

So why am I still alive?It was my boots that saved my life.

Within two hours,the workers removed the tree. Soon the snowstorm calmed downbut not my mother.

Even though she was glad I wasn’t hurt,my mother was still serious. After all,I shouldn’t have brushed off my friend’s warning.

Through this experience,I learn it’s important to listen to people who offer a different perspective. Taking time to listen might actually save a lot of time and trouble. It certainly would have kept me from getting the “shock” of my life.

小题1:The underlined word “disregard” in the second paragraph means “________”.

A.pay no attention to

B.take notice of

C.consider

D.follow小题2:Which of the following statements is NOT true according to the passage?

A.But for his boots,the author would have died.

B.The author regretted having brushed off his friend’s warning.

C.The author knew nothing about electricity.

D.When the tree was cut down,the author realized his friend was right.小题3:The underlined part “the snowstorm calmed down—but not my mother” means “________”.

A.my mother was still angry with me for not listening to my friend’s warning

B.my mother was still in fear of the terrible accident

C.my mother was still comforting me

D.my mother was still worried about my safety小题4:The author wrote the passage mainly to________.

A.give an account of one of his terrible experiences

B.make us know it’s important to listen to people who offer a different perspective through his experience

C.tell us not to cut trees down any more

D.remind us to be careful while we are working