a blue moon

汉语翻译

例句：

1. Barry only visits his parents once in a blue moon.
   巴里很难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.
   河水一旦泛滥，这片园子就会淹没，但这种情况极为罕见。
3. I see her once in a blue moon.
   我难得看到她。