的老师先计划好他的课程，所以每节下课前几分钟，他会利用交接时间前，把下节课需用的东西准备妥当。

The proactive teacher has planned her lessons so that she has a few minutes at the end of each period to get things ready for her next class before passing time.

youdao

In contrast, if we talk about a double bond, what we're now talking about is having both a sigma bond and also one pi bond. And I apologize, I intended to set this up right before class, but that didn't happen today.

相反，如果我们讨论一个双键，我们现在讨论的是,一个sigma键和π键，抱歉，我应该在课前就把这个装好的，今天没装好。

麻省理工公开课 - 化学原理课程节选