Answer:
Domain will be all positive numbers.
Therefore Option D is correct.
Step-by-step explanation:
A tire is of circular shape so the circumference of a circle we know which is:

Where, C is circumference,, r is radius
So, Here the circumference of tire will also be: 
Domain is the value that x will take
And here r is corresponding with r.
So, radius cannot be negative,
So, Domain will be all positive numbers.
Therefore Option D is correct.