习语口语对话大全(MP3+中英字幕) 第247期:once in a blue moon
once in a blue moon
A:The river is much higher than the ground.
A:河比地高得多。B:How dangerous!
B:多危险呀!
A:Yes, it is.
A:是呀。B:What if the river overflowed its bank?
B:河水要是涨过了岸，怎么办?A:That would be disastrous.
A:那可遭殃了。B:The whole city will get flooded?
B：整个城市就会被水淹了?A:Of course. But that happens only once in a blue moon.
A:就是，不过那百年也不见得会遇上一次。
