千载难逢--------It only happens once in a blue moon
例句:
A: Let's go to the megastar's singing performance, shall we?
我们去听那个天王巨星的演唱会,好吗?
B: Why not? It only happens once in a blue moon.
好啊!那可是个千载难逢的机会。
同义词:
It chances in an hour that happens not in seven years