Which weapon was a primary cause of the u. s. entry into world war i? a. nuclear bomb b. machine gun c. submarines d. poison gas

c.submarines

why?

Germany broke its promise to the United States to stop attacking passenger ships (unrestricted submarine warfare). German leaders knew America entering the war would increase the strength of Allied Powers.

its main object was the establishment of "settlement houses" in poor urban areas, in which volunteer middle-class "settlement workers" would live, hoping to share knowledge and culture with, and alleviate the poverty of, their low-income neighbors.