题干

戴眼镜的同学从寒冷的室外进入温暖的室内时,眼镜片上会形成“小水珠”.下列现象中的物态变化方式与“小水珠”形成原因相同的是(  )

A:从冰箱取出的冻肉会变软

B:初冬的清晨,鸭绿江水面上飘着“白气”

C:人游泳之后刚从水中出来,感觉冷

D:教室内,用久的日光灯管两端会发黑

上一题 下一题 0.0难度 选择题 更新时间:2012-11-19 11:52:57

答案(点此获取答案解析)

B

同类题2

阅读庞之浩的《激光是太空垃圾的“清道夫”》一文,完成后面小题。
       ①据最新报道,澳大利亚目前正在研发一种用激光处理太空垃圾的新方法,即从地球上发射激光来分解绕着地球转的太空垃圾,以减少其可能引发系列撞击事件。
       ②自1957年人类发射第一颗人造卫星至今,各国已发射了5000多颗卫星、火箭、探测器等航天器,同时形成了3000多吨围绕地球飞行的太空垃圾。而且,这一数量每年还在以2%—5%的速度增加。太空垃圾在太空中以每秒6000至7000米的速度运行,相对速度很高,潜在危害极大。一个仅10克重的太空垃圾所产生的撞击能量,相当于时速100千米行驶的两辆轿车迎面相撞产生的能量。目前,在各国正在探索的清理方式中,激光算得上是最可行的方式之一。
       ③用激光清除太空垃圾主要有两种方式:直接烧蚀式和烧蚀反喷式。前者可用于清除微小太空垃圾,即利用强大的连续波激光照射太空垃圾,把光能转化为热能,使其温度升高至垃圾碎片的熔点甚至沸点,使其被熔化和汽化,实现碎片清理;烧蚀反喷式主要用于清除较大的太空垃圾,它是用高能脉冲激光束照射太空垃圾表面,产生类似于火箭推进的“热物质射流”,为太空垃圾提供一定的速度增量,从而使其近地点高度降低以致进入大气层摩擦烧毁,以达到清除空间轨道碎片的目的。
       ④激光清除太空垃圾可采用不同的平台,主要有地基、空基和天基激光器等。天基激光器一般被部署在卫星上,由于激光在真空中传播时的损耗可忽略不计,没有折射、散射等传播误差影响,其实用空间范围得到了扩展。天基激光是未来清除太空垃圾的一种高效方案,但也有科学家认为,这种激光可能演变成一种“空间武器”。
       ⑤对付太空垃圾是一项多学科的综合性长期工作,需要各国的重视,需要广泛的国际合作。只有群策群力,人类才能拥有清洁、安全的太空环境。

同类题3

阅读理解

    Most people say that most people have not more than 30 friends at any given time, and 400 over the whole of their lives. However, on social networking sites, most users have about 150 friends. If these numbers are correct, then friendship means different things in different situations.

    Also, there are no rules about friendship. There are no instructions about how to make friends, how to keep friendships going, and how to finish friendships if we want to move on. People have very different opinions about this: some people would die for their friends and they value them more than family. Others say that friends are temporary, only there to help each other until they are no longer needed. If people with such different views become friends, this can lead to problems.

    Because of these different definitions of friendship, it is easy to be unhappy about our friendships. We may want them to be deeper or closer, or we may want to have more friends in our lives. Sometimes we simply do not have the time to develop our friendships, or we fear we have left it too late in life to start. If we move to another country or city, we have to find ways, to make new friends again.

    This dissatisfaction shows us how important friendships are for most of us. We should not think that it could be too late to build friendships. We also need to understand that the need to be around other people is one that is shared by many. Therefore, we should not be too frightened about starting to talk to people who in the future may become our friends: it is likely that they too would like to get closer to us. Remember what people say: strangers are friends we have not met yet.