Governments can manage the affairs of a large group of people by a. providing firefighting services b. providing public libraries c. raising militaries d. signing international treaties

D. signing international treaties

Explanation:

The governments are the bodies that control the countries, thus they are the ones that also control large groups of people that live in those countries. The different groups of people don't always agree with each other, and very often there are tensions between them, and even hostility, and the sources of that are many.

One of the purposes of the governments is to be able to manage the affairs of the large groups of people. The managing of the affairs is supposed to be in a peaceful manner, so to avoid casualties, military conflicts, or economic problems. In order to do so, the best way and most used way used by the governments is to negotiate and sign a treaty. By signing a treaty, the governments obligate themselves to certain things in order for the situation to be stable, and the relations between the countries, and the groups of people for that matter, to be good and to move into a positive direction.

the answer is crop rotation