During the Spring and Autumn Period, the agricultural production was highly subject to the seasonal changes with the invention of iron tools, thus forming the concept of Solar Term.
春秋战国以后随着铁制农具的出现，农业生产对季节性的要求更高了，就逐渐形成了节气的概念。
2
In the northern hemisphere we are now entering the peak period for seasonal flu.
在北半球，我们现正进入季节性流感的高峰期。
3
The incubation period for H5N1 avian influenza may be longer than that for normal seasonal influenza, which is around two to three days.