The Text Discussed Research to Establish If There Was a Causal

The text discussed research to establish if there was a causal relationship between cell phone use while driving, traffic density and increased risk of vehicular collision. Which of the following accurately describes the independent and dependent variables in this research?

A) Traffic density is the independent variable, and cell phone use and risk of vehicular collision are the dependent variables.
B) Risk of vehicular collision is the independent variable, and cell phone use and traffic density are the dependent variables.
C) Cell phone use and risk of vehicular collision are the independent variables, and traffic density is the dependent variable.
D) Cell phone use and traffic density are the independent variables, and risk of vehicular collision is the dependent variable.