The barriers to unity presented by European geography and very limited technology made it hard for a would-be conqueror to create a vast empire, eliminating competitors and imposing his will over vast areas.

由于欧洲独特的地理条件,和当时有限的科技水平,使未来的征伐者很难建立一个广袤的帝国,清除异己和使他的意志,传播到广袤领地的每一个角落

耶鲁公开课 - 古希腊历史简介课程节选

You know this, you can - it's hard to pick up a newspaper or a news magazine without hearing some new application of DNA technology.

你知道的,你-,随便翻一份报纸或杂志,上面很少没提到DNA技术的某个新应用

耶鲁公开课 - 生物医学工程探索课程节选