词典释义：
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Yeah, but he did have to have a bunch of stitches and he said that only once in a blue moon does a dog's ear grow back, so still hoping.
可是他必须帮它缝好多针，而且他还说只有出现蓝月亮时狗才会再长出耳朵来的，所以还有一点点希望。
《Friends Season 2》《老友记 第二季》
双语例句
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The story is just a blue moon.
这个故事根本就是件不可能的事。
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This is a chance in a blue moon.
这可是个难得的机会。
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She visits us once in a blue moon.
她难得来看我们一次。
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It is a chance once in a blue moon.
这是一个千载难逢的好机会。
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But what is a blue moon?
但是什么是蓝月亮呢？