30.High School English Listening

Are aliens going to eat us?
That's more of a science fiction question.
But science does havesomething to say here, and sometimes purely imaginativequestions are great tools for helping us think about how the realworld works.
First, it's not strictly impossible.
Many scientists agree that theMilky Way galaxy is probably brimming with living things.
That doesn't mean any of them aresmart enough to build interstellar spaceships, but let's assume they are.
Still, why are theyunlikely to eat us?
One reason lies in energy itself.
The point of eating is to take in usable energy.
A lion will expend a lot of energy running down azebra because, once it is caught, the calories contained in the meal far outweigh those expended in the chase.
If this weren't true–say, if the zebra's body only had the caloric contentof a grape–then the energy expended would outweigh the energy gained, and the lion wouldlose out.
Any alien predators would face the same problem.
The amount of energy expended in building aspace program, fueling rockets, to say nothing of getting from one star to another, would behuge.
For any realistic technology it would far outweigh the benefit of just munching on people.It would be like climbing Mount Everest in order to pick a few berries.
Some day we ourselves may travel to other planets. But any species that goes to such lengthsmerely to find food will find itself quickly exhausted.
译文：
外星人会吃掉我们吗？
这更像是一个科幻小说的问题。
但科学在这里确实有话要说，而且有时纯粹的想象性问题是帮助我们思考现实世界如何运作的伟大工具。
首先，严格来说，这并不是不可能的。
许多科学家同意，银河系可能充满了生物。
这并不意味着它们中的任何一个都聪明到可以建造星际飞船，但让我们假设它们是。
然而，为什么它们不太可能吃我们呢？
一个原因在于能量本身。
吃东西的意义在于摄取可用的能量。
一头狮子会花费大量的能量去追赶天鹅，因为一旦它被抓住，食物中所包含的热量远远超过了追赶过程中所消耗的热量。
如果这不是真的，比如说，如果斑马的身体只有葡萄的热量，那么消耗的能量就会超过获得的能量，狮子就会输掉。
任何外星捕食者都会面临同样的问题。
建立太空计划，为火箭提供燃料，更不用说从一个星体到另一个星体所消耗的能量将是巨大的。
对于任何现实的技术来说，这将远远超过仅仅啃食人类的好处。这就像为了采摘一些浆果而攀登珠穆朗玛峰。
有一天，我们自己可能会去其他星球旅行。但是，任何物种如果为了寻找食物而大费周章，都会发现自己很快就会筋疲力尽。
重点词汇：
science fiction 科幻小说
think about 考虑 ; 思考 ; 探讨 ; 为…费心思 ; 想像
brimming 满，盛满 ; brim的现在分词
living things 生物
enough to 足够…去做 ; 足以 ; 足够……可以
spaceships 宇宙飞船 ; spaceship的复数
take in 收留，收容 ; 带走，抓走 ; 欺骗 ; 使上当 ; 理解 ; 领会 ; 领悟 ; 看清，看明白 ; 观看 ; 欣赏 ; 参观 ; 摄入，吸收 ; 将改小 ; 收入，进账
a lot of 很多 ; 许多
running down 全熔化
expended 花费 ; 消费 ; 耗费 ; expend的过去分词和过去式