But I was convinced I'd hear the click-click-click-click-click which is what tells you you're in trouble.

我总会觉得很紧张，我不知道这是为什么,虽然我从来没有接触过放射元素。

麻省理工公开课 - 化学原理课程节选

The third derivative, unfortunately, was never given a name, and I don't know why.

遗憾的是三阶导数没有专门的名称,我也不知道这是为什么

耶鲁公开课 - 基础物理课程节选