Does Eating While Driving Make an Accident More Likely? Researchers

Does eating while driving make an accident more likely? Researchers from the National Highway Traffic Safety Administration looked at national traffic and accident records from a recent year for those drivers who were eating versus those who were not. Result: The odds of an accident were 80 percent higher when eating than when not.
The explanatory variable in this study is:

A) whether the subject had an auto accident.
B) whether the subject was eating.
C) the risk of an accident.
D) whether the subject owned a car.