Once the existence of this wave-length had been discovered, it was not long before its use as the uniquely recognizable broadcasting frequency for interstellar communication was suggested.

Once...  ^{一旦…；当…时候}

• Once the ancient map had been discovered, the treasure hunt began in earnest.^{一旦这张古老的地图被发现，寻宝活动就正式开始了。}
• Once you understand the basic principles of AI, you can start building your own tools. ^{一旦你理解了 AI 的基本原理，你就可以开始构建自己的工具了。}

Without something of this kind, searching for intelligences on other planets would be like trying to meet a friend in London without a pre-arranged rendezvous and absurdly wandering the streets in the hope of a chance encounter.

without ^{代替if引导原因状语（从句）}

• Education, … what would civilization be like without its benefits? 
• Without it we could not make a living.
• Without it, nothing could ever be brought to a conclusion; everything would be in a state of chaos.
• Without something of this kind to guide us, the research could wander aimlessly for years.^{没有这种类型的东西来指导我们，这项研究可能会漫无目的地进行数年。}

intelligence ^{n. [C] an intelligent being 智慧生物}

• Yet those forces must be natural; they cannot be attributed to the actions of mysterious creative intelligences whose existence, in scientific terms, is unproved.
• It may exceed human intelligence sooner or later. ^{它迟早会超越人类的智力。}

pre-arranged ^{adj. planned or arranged in advance 提前计划或安排好的}

• The spy operated without a pre-arranged rendezvous, relying solely on cryptic messages.^{这名间谍在没有预先安排好的会面地点的情况下行动，完全依赖于神秘的信息。}
• An interview schedule is typically pre-arranged, and can involve anywhere between 2-5 persons a day; ^{面试时间一般是预先确定的，一天面试人数为2到5人；}
• Click to place blocks in a pre-arranged formation. Current shapes include Round, Square, and Diamond. ^{通过点击来以预定义的结构放置方块。结构可以是圆形，方形和菱形。}

rendezvous ^{n. (pl unchanged 复数不变) (place chosen for a) meeting at an agreed time 约会（地点）}

• arrange / make a rendezvous with Bill at the pub at two o'clock
• He failed to keep a rendezvous after sensing a police trap. ^{他觉察到是警察的圈套后，就未去赴约。}
• She is lured to a rendezvous near Lao Cai to be drugged. ^{她被引诱到老街附近的一个约会地点，并被下了药。}

wander ^{vi./vt. 漫无目的的走，闲逛}

• The dogs have greater freedom, too, for they are allowed to wander outside their enclosure. 
• He was found wandering the streets of New York.
• I've spent two years wandering the world.
• After getting lost, we found ourselves absurdly wandering the streets in the wrong direction.^{迷路后，我们发现自己荒谬地在街上游荡，走错了方向。}

in the hope of sth. / that ... ^{because of the wish for sth. / that ... 怀着…的希望}

• Should they sell now or hang on in the hope that the shares will soon be worth serious money?
• We came to the island in the hope of finding a simpler way of life.

in + 抽象名词 ^{做原因状语（书面语的重要用法）}

• The men of our family waded down through our flooded meadows with boathooks, in the hope of being able to grapple a corner of the raft and pull it out of the current towards our bank.
• Young men who have reason to fear that they will be killed in battle may justifiably feel bitter in the thought that they have cheated of the best things that life has to offer.
• In the lift her thoughts were on lunch and a good rest; but when she got out at her own floor, both were forgotten in her sudden discovery that her front door was open.
• They leave unwanted objects in drawers, cupboards and attics for years, in the belief that they may one day need just those very things.
• The Swedes were the first to recognize that public officials like civil servants, police officers, health inspectors or tax-collectors can make mistakes or act over-zealously in the belief that they are serving the public.

chance ^{adj. [only before noun] not planned or expected = accidental 偶然的}

• The medicine was a chance discovery made by a scientist looking for something else. ^{这种药物是一位科学家在寻找其他东西时的一个偶然发现。}
• A chance meeting / encounter at a tech conference led to their successful business partnership. ^{在一次技术会议上的偶然相遇促成了他们成功的商业合作。}
•  Whether life began through a chance event or a directed process is a major scientific question. ^{生命是通过偶然事件还是通过有向过程开始的，是一个重大的科学问题。}

encounter ^{n. a meeting, esp. one that is sudden, unexpected or violent 偶遇，遭遇，邂逅}

• Three of them were killed in the subsequent encounter with the police.
• The story describes the extraordinary encounter between a man and a dolphin.
• She attended the conference every year in the hope of a chance encounter with her mentor.^{她每年都参加会议，希望能偶然遇到她的导师。}