Answer:
Volunteering to plant trees.
Step-by-step explanation:
One distinct characteristic of a social duty is that it need to be carried out by individuals to benefit the society as a whole. Not just the individuals themselves.
People have their own personal gain when they go out to Vote or promote a certain laws. They're most likely vote for the candidate that they like and promote laws that they will benefited them in some ways.
Planting trees on the other hand, will benefited the society as a whole. It provided a protection to climate change and replenish the source of fresh air that can be consumed by all the people in that community.