Answer: Choice A) x < 7
Reason:
The domain is the set of allowed x inputs.
The graph shows an open hole at x = 7, meaning that 7 itself isn't part of the domain. But any value smaller than this will be part of the domain. So that's why we go for x < 7.
The value x = -1 is allowed since we have a closed endpoint for one of the pieces here.
The arrow pointing to the left indicates that piece goes on forever in that direction.