Our immune system's function is to keep us healthy in the face of an environment where there are lots of things that could potentially harm us.

我们免疫系统的功能就是保持自身健康,在面对危机四伏的环境时,使我们免受伤害

耶鲁公开课 - 生物医学工程探索课程节选

But it's safe and there's no need to feel unsafe.

但是这里很安全，没必要感到危机四伏。

对纽约的印象 - SpeakingMax英语口语达人

The reason for that I think is that the early times in which these civilizations arose saw all kinds of dangers coming, and the most--the swiftest, the least suspected, the one that could come upon you overnight came from the sea.

在我看来原因是,在这些文明所诞生的早期世界危机四伏,而来的最迅速,最难以预测,最可能,一夜之间骤然降临的灾难,正来自于海上

耶鲁公开课 - 古希腊历史简介课程节选