Answer:
a. "Safety in numbers"
Explanation: They stayed in wagon trains together to be more protected and to make sure no one got stolen by Native Americans.
Trench Warfare was a form of military conflict in which opposing sides fought one another from trenches facing one another. WW1 warfare introduced the first large-scale use of chemical weapons as well as bringing in airplanes and tanks for the first time.
I am not sure what the others thought about it (for example Kahlo and Rivera were communists, so they likely believed it too!)
but a very good answer is <span>B. David Alfaro Siqueiros, since he was very opened about this view, stating it many times. </span>
It got larger and more states and colonies were discovered
