题干

以下运动物体可视为质点的是

A:研究和观察日食时,可以把月亮看成质点

B:研究地球自转时,可以把地球看成质点

C:裁判员眼中的跳水运动员

D:火车从上海开往北京,在计算其行车的时间时

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答案(点此获取答案解析)

D

同类题3

阅读《沙滩上的童话》片段,回答问题。

    这里是我们快乐的天地。

    在沙堆上我们垒起城堡,城堡周围筑起围墙,围墙外再插上干树枝,那是我们的树。

    不知谁说了一句:“这城堡里住着一个凶狠的魔王。”

    有人接着补充:“他抢去了美丽的公主!”

    第三个小伙伴说:“你们快听,公主在城堡里哭呢!”

    “就这样,我们编织着童话。”

    转眼间,我们亲手建造的城堡成里一座魔窟,我们也成了攻打魔窟的勇士。

    我们有在一起商量着怎样攻下那座城堡。

    一个伙伴说:“我架驶飞机去轰炸。”

    有人反驳说:“那时候还没有飞机呢!”

    我说:“挖地道,从地下装上火药,把城堡扎平。”

    我的方法得到了大家的赞赏。于是我们趴在沙滩上,从四面八方挖着地道。

    挖呀,挖呀,终于挖到了城堡下面,然后用手往上一抬,就把城堡轰塌了。

    我们欢呼着胜利,欢呼着炸死了魔王,欢呼着救出了公主。

    但公主在哪儿?

    忽然,我发现妈妈就在我们身后,微笑着望着我们。

    我大声说:“公主被我们救出来了,救出来了!在这儿,在这儿!”我抱住了妈妈。

    大家跟着我一起叫喊着,欢呼着。

    真的,那时候,连我也忘记了她就是我的妈妈呀 !

同类题5

阅读理解American Country Music
    Over the past twenty years, American country music has become more and more popular. Song writers are no longer writing about the modern values of the USA—money, success or expensive things to buy. Instead they are writing once more about things that are common for everyone: feeling alone in the modern world, the value of having good friends and so on.
    In the 1950s, American music was about other things, for example, love—getting or losing a boyfriend or girlfriend. Money was also thought to be important.
    Then in the 1960s, song writers turned to other subjects. During these years many young students were angry with society, so songs were often full of anger. Political leaders were not well thought of and those songs often made fun of them.
    Today country music has returned. It has become big business and brings in between 200 and 400 million dollars a year. Once, the home of American country music was Nashville, Tennessee. Now, however, the music has reached all parts of the States, from Los Angeles in the west to New York in the east. Singers do not just come from the States but from all over the world.  There are many famous singers from Britain, Canada and Australia. A lot of them appear on television too.
    The first country singers sang while playing the guitar. It was easy for them to carry a guitar on their travels. Now, however, a lot of electrical equipment is needed for large theatres.
    Country music today remains much the same as before. One subject to which country music often returns is “the good old days”. In “the good old days” people thought well of each other. People loved life in the open air. They believed that the best things in life were free: sunshine, laughing, walks in the beauty of the country, friends and music.