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.

The explanatory variable is the factor used to explain or predict a change in another variable. Here, the technicians noticed that tire tread depth changes with the number of miles on the odometer, so mileage is the explanatory variable and tread depth is the response variable. Choice C states this relationship.

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