1 on a cloud
On a cloud是很高兴的意思，高兴得走路轻飘飘，好像腾云驾雾一样。
例如：I've been on a cloud all day long--I heard this morning that I got an A on my final biochemistry exam.
我今天一天都很高兴，因为我早上听说，我生化期末考试得了一个A。
又如：My wife has been on a cloud since I told her the other day I would spend my year-end bonus at the office to take us to Hawaii to celebrate our twentieth wedding anniversary. And to tell you the truth, I'm really looking forward to it myself.
我那天告诉我的妻子，我要把办公室发给我的年终奖金用来和她一起去夏威夷旅行，以庆祝我们结婚二十周年。自从那天起，我太太一直很高兴。说实话，我自己也非常想去。
2 under a cloud
任何人under a cloud是绝不会高兴的，因为他不是丢尽了面子，就是被怀疑做了什么坏事。Under a cloud是丢面子、被怀疑的意思。
下面是一个人在讲另外一个被逮捕的人，这人被指控和贩毒有关：
The judge had to let him go because there wasn't enough evidence against him. But he's going around under a cloud because most people think he's guilty.
法官由于没有足够的证据来定罪，所以只好放了他。但是，他到哪儿都受怀疑，因为大多数人都认为他是有罪的。
又如：See that man sitting at the table by himself? He's supposed to be a very smart lawyer, but he's been under a cloud ever since he was mixed up in a scandal involving a company that was run by a mobster.
瞧那个桌子边独自坐着的人，看见吗？他本来是一个很能干的律师，但是自从他和一个公司的丑闻有牵连以来，他一直被人怀疑，而那个公司是由流氓集团经营的。
3 in the clouds
我们每个人恐怕都有白日做梦的时候。有的时候，我们一边走路，一边在想心事，或者是一边做什么事，一边在想其他事情，身边发生什么事全然没有注意到。美国人把这叫做：in the clouds。In the clouds可以解释为：心不在焉，思想开小差。
例如：Sally is my best friend but she walked right past me today, and didn't even say hello. Her head certainly was in the clouds--she looked like her mind was a thousand miles away.
沙莉是我最好的朋友，可是，她今天在我身旁走过，连招呼都没有跟我打。她肯定在白日做梦，看起来她的心思好像在一千哩以外的地方。
又如：I was really embarrassed--the teacher asked me a question and I didn't even hear him; I was daydreaming and my head was in the clouds.
我当时真是非常难堪。老师问我问题，我根本没有听见。那时，我刚好在做白日梦，思想在开小差。
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