你知道有些时候我们真的很想工作，而有些时候我们会觉得自己像个十足的懒人。

You know there are times when we are really inspired to work, where other times we'll feel like a total sloth.

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而有些时候其实我不必害怕。

Other times I don't need to be scared.

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正规格式有时是有用的，而有些时候不太正规同样有用。

Other times a less formal tone is more useful.

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So, it could be very interesting for all of us to have issues to discuss in class, and quite often some questions are very common and your classmates will be grateful to you that you brought it up.

所以,大家一起在课堂上讨论一些问题,这会非常有意思,还有些时候,你们的问题很普遍,而你的同学会很感激你提出了这个问题

耶鲁公开课 - 基础物理课程节选