Once In A Lifetime是什么意思

Once In A Lifetime一生只有一次的下面是一些例句：It's a once in a lifetime chance。:这是一生难得的机会。She was brought up to believe you fell in love and got married once in a lifetime。:她从小就受这样的教养：认为恋爱结婚一人一生只能有一次。