Answer: y-axis
Explanation:
The equation of the line of reflection is the perpendicular bisector of the segment that connects a point on the preimage and the corresponding point on the image.
For this, we'll consider A(-1, -1) and A'(1, -1).
The equation of this line is clearly y = -1, and its midpoint is (0, -1).
This means the line of reflection will be a vertical line passing through (0, -1), which is the line x = 0, or the y-axis