So, when you think about resonance structures, some students tend to just get confused and be picturing this flickering back and forth.

那么，当大家想象共振结构的时候，有些同学很容易被弄晕,不停地来回想象。

麻省理工公开课 - 化学原理课程节选

That's the finger thing from left finger to right finger going back and forth across the board, never touching a number more than once.

在合并时，我的左手手指,和右手手指来回地在黑板上移动，但对每个数字只会碰到一次。

哈佛公开课 - 计算机科学课程节选