Automobile tires can have a symmetric tread or an asymmetric tread. An experiment is to be conducted to determine whether the stopping distance is the same for both types of tire treads. In previous studies, it was determined that automobile size (small, medium, large) is associated with stopping distance, but automobile type (van, truck, SUV, and so on) is not associated with stopping distance. How could the experiment BEST be conducted?
A. By blocking on stopping distance
B. By blocking on tire tread type
C. By blocking on automobile type
D. By blocking on automobile size
E. Without blocking