https://online2.tingclass.net/lesson/shi0529/0009/9907/231.mp3
https://image.tingclass.net/statics/js/2012
讲解文本：
once in a blue moon 千载难逢，极其偶尔
Mary lives far away, we only see each other once in a blue moon.
Mary住的很远，我们很难见一次。
This kind of chance comes once in a blue moon.
这种机会可是千载难逢!
疯狂练习吧!
