A tire company wants to determine if tires made with a new type of tread will last longer than tires made with the original type of tread. The company has access to 20 different vehicles and wants to use a randomized block design for the experiment.Which of the following variables would be the best to block the experimental units?

A randomized block design groups similar experimental units before assigning treatments. The type of vehicle can affect tire wear because different vehicle types may differ in weight, size, and typical use. Blocking by vehicle type helps control those differences when comparing the new tread with the original tread. Vehicle color is unlikely to affect how long tires last.

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