b) scarcely
Well done ! That’s the right answer.
If something happens ’once in a blue moon’, it happens only very rarely.
French translation
tous les 36 du mois
How NOT to translate : *une fois la lune bleue
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Examples in the press
Once in a Blue Moon : Rare Seasonal Blue Moon to Rise This Weekend
An unusual occurrence in the night sky will take place this weekend, yet it may go undetected by people who don’t know what’s going on.
A full moon will rise on Saturday evening, looking similar to others that rise throughout the year, yet this one will be unlike any other full moon in 2021. The full moon on Saturday night will be a blue moon.
The second full moon in a calendar month is referred to as a blue moon. This happens every two or three years, with the most recent instance being on Halloween last year.
This is how the phrase "once in a blue moon" came to denote a rare occurrence. A full moon, on the other hand, might earn this moniker in another way.
Nature World News, 20 August 21
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Everyday usage
John only comes out for a drink once in blue moon now that he has children.
Only once in a blue moon do properties of this quality become available.
– A : ‘Do you eat pork ?’
– B : ‘Only once in a blue moon’. I am a flexitarian ».
EnglishTonic and Claramedia, 27 September 2021
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