Answer: Choice C)
The domain is the set of possible x values or allowed inputs. The left-most point has x = -6 as the smallest allowed x value, while the right-most point has x = 2 as the largest allowed x value.
The domain is the set of numbers between -6 and 2, including both endpoints. So we write
If you want the domain written in interval notation, then you would have [-6, 2]. The square brackets tell the reader "include the endpoint".