So you can think of it, if we were to just think of it as a straight line that we were going across, essentially what we're saying is that we're getting from point a to point c without ever getting through point b.

你们可以来想想看，如我我们把它想成是一条直线,我们要沿着这条线经过，这就是说我们要从ａ点,不经过ｂ点而到ｃ点。

麻省理工公开课 - 化学原理课程节选

Press your lips together with the corners straight or down.

把嘴唇并在一起，嘴角成一条直线，向下。

耶鲁公开课 - 心理学导论课程节选