And the obvious question I could start with is, and suppose I ask you, how long does the algorithm implemented by this program take to run?

我开始这个话题的第一个问题是，假设我问你，由这个算法实现的程序大概,要运行多久才能给出答案？

麻省理工公开课 - 计算机科学及编程导论课程节选

I need to know how long, so that I can let my roommates know.

我得知道大概有多久，这样我就可以告诉我的室友们了。

How long实战 - SpeakingMax英语口语达人