Final answer:
Community support and charitable donations were the most instrumental factors in the growth of nonprofit community hospitals in the United States, creating a robust network of local resources and service providers to address healthcare needs.
Step-by-step explanation:
The factor that was most instrumental in the growth of nonprofit community hospitals in the United States was b) Community support and charitable donations. This community-driven model has historically been the foundation on which many nonprofit health organizations have been built, relying on the generosity and support of local residents, philanthropic entities, and charities rather than on strictly profit-driven motives, corporate sponsorships, or direct government mandates. While governmental agency involvement and policies have played roles in shaping the healthcare landscape, it is the involvement and support of the communities that have fundamentally sustained and propelled the growth of these healthcare institutions.
In understanding the impacts of various factors on nonprofit hospitals, it's essential to recognize that local support can help address resource gaps, especially in underserved or economically challenged areas. Additionally, collective efforts in a community can create a strong network of service providers and maintain connections that are vital for the survival of nonprofit entities, which tend to operate with a strong sense of mission to serve their patients over profit maximization.