once in a blue moon 帮忙用这个造俩句子,

once in a blue moon:千载难逢；极为罕见It snows here once in a blue moon.这里几乎不下雪.（这里很长时间才下一次雪.）This is a chance once in a blue moon.这是一个千载难逢的好机会.There is a chance once i...