Remember the domain of a function is the values of x for which the function is defined (exists)
Notice that if x is less than 0, there's no graph. (Function isn´t defined for x<0)
That little filled ball in the begining of the graph is telling us that the function is defined for 0. If it wasn't, the ball would be empty.
With this info, we can conclude that the function is defined for x equal or greater than 0
Therefore, the domain of the function is:
(Option A)