a blue moon

漢語翻譯

例句：

1. Barry only visits his parents once in a blue moon.
   巴里很難得去看望他父母一次。
2. If the river overflows its banks, the garden gets flooded; but that only happens once in a blue moon.
   河水一旦泛濫，這片園子就會淹沒，但這種情況極為罕見。
3. I see her once in a blue moon.
   我難得看到她。