This sort of opportunity comes along once in a lifetime. = This is a once-in-a-lifetime opportunity.这种机会一生中只会出现一次。The visit to Tibet was a once-in-a-lifetime opportunity.这次去西藏是一次千载难逢的机会。A tour of Australia is a once-in-a-lifetime experience.澳大利亚之行是一生难得的一次经历。