In The Johnstown Flood, how does the author develop the idea that people's decisions to stay or to flee determined whether they lived or died?

O by switching from scene to scene, showing the lives of different members of families
O by giving examples of several people who lost their lives after deciding to stay where
they were
O by listing the cause of death of everyone who was lost in the flood
O by following one person-Gertrude—and her decisions and their effects