Answer:
1) Physicochemical stressor
External environment represented by "nature." For example, change in climate and weather.
Pollution, disaster, and chemical substance are also in this category.
2) Social stressor
The "social environment." For example, change in economic condition, international position of a country are them. On individual level, life environment such as work, home, and school, human relationship.
3) Biological stressor
The internal environment. Some change occurred inside our body. Sickness and injury would be the easiest example for this. Others include fatigue, lack in sleeping time, time rag, etc.