如何表达“千载难逢；极为罕见”呢？

once in a blue moon

very rarely

很少

once after a long time

很久之后

something that happens very seldom

很少发生的事情

如何运用：

I heard Kim became a membership in the gym.

I don’t know why he bought that membership card, he uses it once in a blue moon.

我听说Kim成为了健身房的会员。

我不知道他为什么买那张会员卡，他基本不用的。

跟读练习：

I think my grandson doesn’t love me anymore, he comes to see me only once in a blue moon.

我想我的孙子不再爱我了，他很久都不来看我了。