Answer:
C. They provided schools, hospitals, and centers of hospitality for travelers.
Step-by-step explanation:
Option "A" mentions monasteries only as learning centers, not to mention that they have been directed to the community service.
Option "B" and "D" say that the monks and nuns made vows of poverty and that they were very kind people but doesn´t describe the way in which the monks and nuns were social workers in their community.
Finally, option "C" refers to the fact that the monasteries provided schools, hospitals and hospitality centers for travelers, and that is why it best describes the ways in which the monks and nuns dedicated themselves to social work in their communities.