They are serious and they are many. They will not be met easily or in a short span of time.

VOA: standard.2010.01.15

But if you think of the time span about 900 to 700 B.C., that is, when these changes are taking place.

但是如果你发现它发生在,大约公元前900年到700年之间时

耶鲁公开课 - 古希腊历史简介课程节选

I've made a lot of really good friends in a really short time span.

在很短的一段时间里，我就交了很多好朋友。

斯坦福的奖学金 - SpeakingMax英语口语达人