Answer: Check nearly every box except choice A.
Reason:
The domain is the set of allowed x values. We look at the x coordinates of each point on the red curves.
x = 2 isn't allowed since drawing a vertical line from x = 2 on the x axis does not lead to any piece of the red curve. Therefore, x = 2 is not in the domain. The other x values mentioned are in the domain.
For instance, start at x = 4. Draw a vertical line through there. That vertical line crosses the red curve at exactly one point. This visually confirms x = 4 is in the domain. That means choice E is one of the answers. Choices B, C, D, and F are similar stories so they are also answers.
Note: the closed endpoints indicate "include this x value in the domain". We will include x = 4 and x = -4 in the domain.