Okay, if anybody has questions about this one in particular you can ask Christina after class or at a different time.

如果大家有问题想单独问她,可以在下课后或其他时间问她

耶鲁公开课 - 关于食物的心理学、生物学和政治学课程节选

whenever you want to express what you are doing at a particular moment in time.

当你想表达在某一时刻你在做的事情时，你都可以用这个句型。

I'm ~ing 课堂 - SpeakingMax英语口语达人

That is basically saying, given some collection of data, I want to have again a looping mechanism, where now my process is, walk through this, the collection one element at a time. And for that, we have a particular construct, called a FOR loop.

现在我的过程就是,通过一个个访问这个集合中,的元素的方式，来遍历这个集合,为了达到这个目的，我们有一个特定的结构，成为FOR循环。

麻省理工公开课 - 计算机科学及编程导论课程节选