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

So one of the reasons there is a huge increase in life span is because people aren't dying of things that they would have in prior years.

寿命范围显著增长的一个原因是,人们不再死于,以前那些致死的东西

耶鲁公开课 - 生物医学工程探索课程节选

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

Here in the U.S., the rate of obesity doubled over a span of 16 years.

VOA: standard.2010.08.10

The expected life spans increased dramatically in the last couple of hundred years until now, for people that were born when you were born you can expect to live to be 80 years old, a doubling in life span, fairly dramatic.

从几百年前到现在,预期寿命显著增长了,你们同期出生的那批人,能够活到八十岁,预期寿命增长了一倍,令人印象深刻

耶鲁公开课 - 生物医学工程探索课程节选