a blue moon

基本解释

If you only send faxes once in a blue moon, do it from Staples or a copy shop.
如果您衹發送傳真一次在一藍色的月亮，也從史泰博或複印店了。
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You should be grateful for the extra job offer. Things like that come along only once in a blue moon.
你應該對額外的工作機會抱有感激之心：這樣的事可是極其難得。
He’s the kind of player that comes along once in a blue moon, a play maker whose vision, passing and inventiveness makes a huge impact on any game he plays in.
他是那種百年不遇的天才球員。作爲球隊的核心，他的眡野，激情以及創造性都會對比賽産生巨大的影響。

Occasionally it will be hundreds of millions and once in a blue moon billions.
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And then, every once in a blue moon, something comes along that is in a category all its own.
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Once in a blue moon, he tells me, he saw an iPhone.
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