Auto technicians working at a shop in a rural residential area noticed that the depth of tire treads was smaller among cars that have more miles on the odometer. What are the explanatory variable and response variable for this relationship?

Explanatory variable: type of residential area

Response variable: depth of tire tread

Explanatory variable: depth of tire tread

Response variable: miles on the car odometer

Explanatory variable: miles on the car odometer

Response variable: depth of tire tread

Explanatory variable: type of residential area

Response variable: miles on the car odometer

I think its, (B):
Explanatory variable: depth of tire tread

Response variable: miles on the car odometer