The flu, by comparison, has an average incubation period of just two days.

相比之下，流感的平均潜伏期 只有短短两天的时间。

In the agriculture period, average age is like a 30, 35 years old.

农业时代，人类的平均寿命大约在30～35岁。

This year's Northern Hemisphere summer was the hottest ever, with August about 1.5 degrees Celsius warmer than pre-industrial period averages.

今年北半球的夏天是有史以来最热的，八月份的气温比工业化前的平均气温高出1.5摄氏度。

Because some students attend college and others don't, let's just assume an average period of 15 years spent in school.

因为有些学生会上大学，有些则不会，我们就假设平均在校时间为 15 年。