环游世界是一次宝贵的机会。

A trip round the world is a ___priceless opportunity.

如果我的朋友错过这个独特而宝贵的机会，那将是一种遗憾，甚至是不公平的。

It would be sad if not unfair for my friend to miss this unique and ___priceless opportunity.

他在该领域的经验对研究团队来说是无价的。

His experience in the field proved to be ___priceless for the research team.