Christmass comes but once a year.
圣诞节一年只有一次。
But once a couple is living together, it is harder to split up than if they were merely dating.
但一旦双方住在一起，同当初简单的约会相比，就更难以分开。
I've found email is a good way to initiate contact, but once a conversation starts it's a bad medium.
我发现电子信函是发起联系的好方法，但是一旦交流开始，它就是一个很糟糕的工具。
Most ones that I know have very high ethical standards, but once a VC has heard your idea he can't "un-think" it.
我认识的大多数风险投资人都有很高的道德操守，但一旦风险投资人听到了你的创业点子，就再也无法把它从头脑中抹去。
But once a solid-fuel rocket is ignited, it is off like a firework and keeps going until all the fuel is burned up.
但是一旦固体燃料火箭发动机被点燃，它将象二踢脚一样发射出去并一直跑，直到全部燃料烧完为止。
But once a money is established on the market, then every single exchange includes the money-commodity as one of its two commodities.
而一旦市场里建立起了货币，然后所有的交易都可以简化为“货币——商品”之间的交换，用货币替代另一种商品。
But once a relationship has become long-term, although we still talk about love and commitment, in some ways it's satisfaction that comes to the forefront.
然而一旦交往关系确认成为长期的，虽然我们仍会谈及爱和承诺，对这段关系的满足感却变得重要起来。
For example, I often reward myself on the weekend for a good week of eating healthy and resisting temptations. This is not a daily reward, but once a week.
比如，我会在周末时对自己一周来的健康饮食和控制食欲有所奖赏，这不是每天都有，而是一周一次，同时，我会去跑步（或参加比赛），周日骑单车，整理花园，以此消耗掉周末奖励得来的糖分和脂肪。
But once a craft hits orbit, he says, his new invention makes more sense: The Mini-Helicon Plasma Thruster is designed to be a lighter, cheaper way to move through space.
但是一旦飞船进入太空轨道，他认为他的发明将会更具有现实意义：Mini—Helicon型等离子推进器正是为能更轻巧廉价地在太空飞行而诞生的。
Jupiter, Saturn, Uranus, and Neptune. Those are the gas giants, the four heavyweights of the solar system. But was there once a fifth?
木星、土星、天王星和海王星。这些都是气体行星，是太阳系的四个重量级。但曾经存在第五个行星吗？
Now she attributes much of her understanding of college to that: "But once I got to campus, it was a completely different ball game that no one really prepared me for."
现在她把自己对大学的理解很大程度上归结为：“但一旦我进入校园，一切就完全不同了，没有人真正让我做好准备。”
Andre tells Kim that he once had a sister, but Jack had killed her.
安德烈告诉金姆他曾经有过一个妹妹，但杰克杀死了她。
It may look like a normal yellow bus, but all the magic happens once you get inside.
它可能看起来像一辆普通的黄色巴士，但一旦你进去，所有的奇迹就会发生。
Snow falls as hexagonal crystals, but once on the ground, snow is soon transformed into a compacted mass of smaller, rounded grains.
雪以六角形晶体的形式落下，但一旦落到地面，雪很快就会变成一团更小、更圆的颗粒。
I'm hardly a clotheshorse, but the few new items I buy once again trumped the amount of water flowing from my faucets each day.
我不是一个讲究穿衣的人，但我买的几件新衣服又一次超过了每天从水龙头流出的水量。
I once intended to sell it, but now, I'm thinking of turning it into a guest house, because it's still a solid structure.
我曾经打算把它卖了，但是现在，我想把它改造成一个宾馆，因为它还是一座很坚固的建筑物。
I once sold a set of British furniture to a customer from Japan, but I didn't send him the furniture on time, which made me very embarrassed.
我曾经卖过一套英国家具给一个日本客户，但是我没有及时把家具寄给他，这让我很尴尬。
An episode of major depression may occur only once in a person's lifetime, but more often, it recurs throughout a person's life.
重度抑郁发作可能在一个人的一生中仅出现一次，但更经常的是，它在一个人的一生中反复出现。
Sitting in a more comfortable car in a different traffic jam is pleasant but hardly the liberation that once seemed to be promised.
在另一场交通拥堵中，坐在一辆更舒适的车里是令人愉快的，但难以感觉到曾承诺过的那种自由的感觉。
Perhaps that once was true, but today elderly Americans as a group have a lower poverty rate than the rest of the population.
也许这曾经是对的，但是今天美国老年群体的贫困率比其他人群要低。
There's a chance that eventually we'll return all this kindness with the extravagant spending that was once decried but now everyone is hoping will restart the economy.
最终，我们有可能以奢侈消费来回报这种善意。这种奢侈消费曾经受到谴责，但现在每个人都希望能以其重启经济。
It's hard work, but while you are reading, you'll find that what once seemed like a duty is now a pleasure.
这是一项艰苦的工作，但当你阅读时，你会发现曾经被视为一种义务的事情现在变成了一种乐趣。
Sheep once sold for as little as 50 cents each during a glut in the 1980s, but today some breeds of ewe can sell for as much as $200 a pop.
在20世纪80年代的一次供过于求中，羊的价格一度低至每只50美分，但如今一些品种的母羊可以卖到每只200美元。
A small but vocal group of Hawaiians and environmentalists have long viewed their presence as disrespect for sacred land and a painful reminder of the occupation of what was once a sovereign nation.
一群规模不大但积极发声的夏威夷人和环境保护主义者长期以来一直把这些（望远镜）的存在视作对圣地的不敬，以及勾起他们对曾经主权国家被占领的沉痛回忆的事物。
He once told me that he was very nervous at first. He was not only trying to learn this hard new job but also a new language.
他曾经告诉我他一开始很紧张。他不仅在努力学习这一艰难的新工作，而且在努力学习一门新的语言。
She wore one of his shirts, a shirt that had once been blue but had faded until the color could not be named, and a pair of his breeches.
她穿着他的一件衬衣，这件衬衣曾经是蓝色的，但已经褪得说不上是什么颜色了，还穿了他一条马裤。
Once in a while, I'll listen to the radio to see what they are putting out, but it's not too often I hear something I like.
偶尔，我会听听收音机，看看他们在播什么，但不常听到我喜欢的东西。
They are to be admired and pitied, as one would pity and admire a being at once night and day, without eyes beneath his lashes but with a star on his brow.
我们应当赞美并怜悯他们，正如我们同时日夜怜悯又赞美一个人，在他的睫毛下面没有眼睛，只有一颗星星在额上。
But once out of a job, older workers have a much harder time finding another one.
但是一旦失业，年纪大的工人就很难找到另一份工作。
Pinocchio did not answer, but sighed deeply once--twice--a third time.
皮诺乔没有回答，只是深深地叹了一口气——叹了第二口气——叹了第三口气。
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