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A man trying to see a single atom would be somewhat like a man trying to see a single drop of water in the ocean while flying many miles above it. 一个人试图看到单个的原子，有点像一个人翱翔于茫茫大海之上许多英里的高空而试图看到大海中的一滴水一样。（trying to see a single atom 完全是一种假想的情况）
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The same thing, happening in wartime, would amount to disaster. 同样的事, 要是发生在战争年代, 就会酿成大祸。
H. 并列连词 or, otherwise, else, or else
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When you stand on the ground you are pushing down on it with a force equal to your weight, and at the same time the ground must be pushing up on you with exactly the same force. Or you would fall all the way down to the center of the earth. 当你站在地面上时，你就是在向下对地面施加一个等于你体重的力，与此同时，地面必然向上对你施加一个大小完全相等的力，否则你就会一直掉到地球中心。（Or 提出的是一个与客观事实完全相反的假想情况）
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The thin-film cells must demonstrate an efficiency of at least 10 percent, or else the noncell costs alone would make them too expensive to compete with coal. 这种薄膜电池必须至少有百分之十的效率，否则仅非电池部分的成本就会使薄膜电池的价格变得非常昂贵，以至不可能与煤相匹敌。
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Gas molecules move in all directions, otherwise the color could not spread throughout the jar. 气体分子是到处运动的，不然的话，颜色就不可能扩散及整个瓶子。