Answer: Option A.
Explanation:
For a function f(x) = y, the domain is the set of the possible values of x.
In the image we can see that the graph has two arrows, one pointing to the left and another pointing to the right, this means that the function extends infinitely to both sides.
Then there is no value of x that generates a given problem, then the domain is the set of all real numbers.
The set written in interval notation is:
-∞ < x < ∞
Then the correct option is A.