Answer:
A.ones
Explanation:
Depending on the state and country, cars can have 1 or 2 license plates on them. The one mandatory is in the back. In some places, the cars also have a license plate in the front of the car.
So, since the answer is either 1 or 2, the range for that answer is under 10... so it's a single digit... making it a measure in ones.
The number of tires on a car is also measured in ones.