In Chapter 8, We Mentioned a Study That Examined the Relationship

In Chapter 8, we mentioned a study that examined the relationship between where one lives urban or rural) and when a specific form of cancer is diagnosed.For this example, the independent variable was where one lives.Which statement best explains why where one lives was a between subjects variable?

A) Participants who had lived in both settings were included.
B) The researchers manipulated where the participants lived.
C) Participants could live in both settings.
D) Participants could not live in both settings.