题干

月球上没有空气,若宇航员在月球上将羽毛和石块从同一高度处同时由静止释放,则(  )

A:羽毛先落地

B:石块先落地

C:它们同时落地

D:它们不可能同时落地

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答案(点此获取答案解析)

C

同类题1

阅读下文,回答问题

“两弹元勋"的高尚品格

    ①研制核武器除了连续作战的疲劳和挖空心思地用脑之外,还有一个更可怕的东西,那便是放射性核辐射对人体的伤害。

    ②20世纪70年代末,一次偶然的事故出现了。飞机空投时降落伞没有打开,核弹从高空直接摔倒了地上。天空没有出现蘑菇云,核弹哪里去了?指挥部立即派出一百多名防化兵去寻找。他们来回奔跑在荒无人烟的戈壁滩上。邓稼先决定亲自去找,许多同志都反对。基地司令员陈彬同志出语非常感人:“老邓,你不能去,你的命比我的值钱。”邓稼先为生死与共的同志的真挚情感所打动。但他清楚地知道,放射性钚,在大自然中的半衰期是两万四千年,在人体内的半衰期是二百年,即进入体内后二百年还剩一半,这就是说,它将终生伤害着“吃剂量”(即受到辐射)的人的身体。仅仅一克重的钚就可以毒死一百万只鸽子。邓稼先心里有一句没有说出来的话:“这事我不去谁去?”

    ③他和二机部副部长赵敬璞同行。吉普车在大戈壁上飞跑,终于到了发生事故地区的边缘。一下车,邓稼先坚决阻拦赵副部长和司机与他同行,他急了。忘掉了对领导同志应有的尊重,大声对赵副部长喊:“你们站住!你们进去也没有用!”

    ④这位五十多岁的核科学家、中国核武器理论设计总负责人勇敢地向着危险区走去。终于,碎弹被他找到了,高度的责任感使他在一瞬间变成了一个傻子,他竟用双手捧起了碎弹片——这个含有剧毒的危险的放射物。他立即放心了,他们最担心的后果没有出现。他见到赵副部长的第一句话就是“平安无事”。就在这时,他意识到自己的身体一定是有事了。他主动邀请赵副部长与他合影留念。

    ⑤邓稼先在研制核武器的紧张工作中,从来没有主动邀请别人合影,这次他要特别留下一张纪念照,一定是内心已有了什么想法。他似乎觉察到自己寿命的期限了吧,尽管期限是模糊的,但危险是清楚的。他遭受到极为严重的放射性钚的辐射伤害,这将是他身体健康的巨大转折。这种伤害是现代医学水平无法补救的。

同类题2

阅读下面材料,从每题所给的A、B、C、D四个选项中选出最佳选项。

B

    Language students often think they have memory problems. They worry because they can't remember words. In fact, the problem usually isn't with their memory. The problem is with how they study.

    To remember words better, you need to understand how memory works. There are two kinds of memory: short-term and long-term. When you see, hear, or read something, it goes first into short-term memory. But short-term memory lasts for only a few seconds. You will only remember something longer if it goes into long-term memory. Your long-term memory is like a very big library with many, many books. And like a library, it's organized (有条理的). When you put away a book – or memory – you can't just leave it anywhere. You have to choose a place where you can find it again.

    How can you do this with vocabulary? The answer is to work with the word and think about the word in new ways. You can do this by writing new sentences that include it. Even better, you can invent a little story about the word, with people or places that you know. Another way is to make a picture in your mind with the word. For example, if the word is height, you can think of the tallest person you know and try to guess his or her height. All of these activities are good ways to think about words. They make the meaning of words stronger in your long-term memory. And they give a way to find a word when you need it.