Bicycles have three types of tires: mountain bike, road touring, and cruising. An experiment is to be conducted to
determine whether the mileage before a tire change is needed is the same for all three types of tires. In previous studies, it was determined that bicycle weight (light, normal, heavy) is associated with frequency of tire changes, but bike type (mountain, road, cruising) is not associated with frequency of fire change. How would blocking best be used?
a.) by blocking on bicycle type
b.) by blocking on mileage
c.) blocking is not suggested
d.) by blocking on tire type
e.) by blocking on bicycle weight