如图装置为某学生在科技创新大赛时发明的可以直接测量液体密度的“密度天平”.其制作过程和原理如下：选择一根长1米的杠杆，调节两边螺母使杠杆在水平位置平衡，在左侧离中点10 厘米的A 位置用细线固定一个质量为150克、容积为80毫升的容器。右侧用细线悬挂一质量为50 克的钩码（细线的质量忽略不计）。测量时往容器中加满待测液体，移动钩码使杠杆在水平位置平衡，在钩码悬挂位置直接读出液体的密度。

阅读下列材料，回答问题。

材料一：一般而言，地势越高，气温就越低、，即使在赤道地区，高山的山顶也会终年积雪。地势和地形的变化都会影响山地的气候，因而使植被、农作物和居民的生活方式也发生相应的变化。

材料二：在秘鲁安第斯山区，羊驼和骆马是该地区很特别的牲畜，它们能在海拔3000米～4000米的山区靠粗粮来养活，又能在崎岖的山岭间行走自如，是当地居民主要的运输工具。羊驼和骆马还可为居民提供奶类、肉食和皮革。此外，羊驼出产优质羊驼毛，是世界毛纺织工业的重要原料，是秘鲁重要的出口产品。

材料三：高山的自然环境恶劣，高山空气稀薄，山区气温变化剧烈，即使在夏季，夜间也非常寒冷，冬天时更是寒风凛冽，居民需要披上厚重的披肩或斗篷保护身体，戴羊毛面罩保护脸部，在屋内燃烧木材和动物粪便来取暖。

阅读下文，回答相关问题。

       ①我举起拖舰队来的缆绳的一端，高声呼喊：“最强大的利立浦特皇帝万岁！”这位伟大的君王迎我上岸，对我竭尽赞颂，当场就封了他们那里最高的荣誉称号“那达克” 给我。皇帝的野心很大，他要再找机会把敌人的船舰都拉回他的港口，甚至想把不来夫斯库整个帝国灭掉，划作一个行省，派上一位总督去统治。他想彻底消灭大端派的流亡者，强迫那个国家的人民也都打破蛋的小端，那样他就可以做全世界独一无二的君主。
       ②但是，我尽力设法让他打消这种念头，从政策到正义，我向他列举了许多论据。我坦白地表示，我不愿做人家的工具，使一个自由、勇敢的民族沦为奴隶。这件事在国务会议上辩论的时候，大臣中最聪明的一部分人都赞同我的意见。由于我的这一公开而大胆的声明完全违背了皇帝的计划与政策，他因此永远也不会宽恕我。他在国务会议上以一种很策略的方式提到了这事。据说，最聪明的几位大臣至少是以沉默的方式表示了他们是赞成我的意见。可是另一些人是我的死敌，忍不住就要说话，旁敲侧击地中伤我。从此，皇帝与一小撮对我不怀好意的大臣之间就开始达成一项阴谋；不到两个月，阴谋暴露，却差点儿以我的彻底消灭而告终。最大的功绩在君王眼里又能算什么，你一拂逆他，不使其野心得到满足，再大的功劳也等于零。
                                                                                                           （节选自斯威夫特《格列佛游记》）

阅读下列短文，根据短文内容选择最佳答案。

                                                                           C

    Flying is a fast way to travel. But it is a big headache for some people. They can't help worrying about things like, “Is turbulence (颠簸) a bad thing?” or, “Is it dangerous if we don't change our mobile phones to flight mode (飞行模式)?” British newspaper Daily Mail spoke to some experts to answer these questions. They also tell us other interesting things about flying.

    Is turbulence dangerous?

    It's scary and uncomfortable. But it is not something you really need to worry about.

    Turbulence is caused when two groups of air hit one another at different speeds. Wind, thunderstorms (暴风雨) and being close to mountains can be reasons for this.

    You may feel like turbulence is dangerous, but it won't crash (坠毁) your plane. “Even in extremely rough air (扰动气流), the wings (机翼) are not going to break off,” explained Patrick Smith, an airline pilot, who is also an air travel blogger and author of Ask The Pilot. com.

    Why are plane windows round?

    Round windows are for passenger safety.

    As the airplane flies higher and higher, the outside atmospheric pressure (气压) gets lower and lower. During the flight, the pressure inside the plane becomes greater than the pressure outside.

    When this happens, square windows can break. That's because having different pressures inside and outside puts pressure on the corners of square windows. But rounded corners can spread the pressure through the window.

    What happens when a phone isn't on flight mode?

    Some passengers believe mobile phones and tablets need to be turned off because they could bring the plane down. However, this is not true.

    If you don't change your phone to flight mode, pilots and air traffic controllers may hear unpleasant sounds in their headphones. It also influences radio communications. So it's still best to put it on flight mode.