Final answer:
None of the given choices correctly maps square ABCD onto itself. The correct line of reflection should be x = 2, which is not listed in the options.
Step-by-step explanation:
The line of reflection that would map square ABCD onto itself, given that C is at (1, 3), D at (1, 1), A at (3, 1), and B at (3, 3), would be a line that passes through the midpoints of the opposite sides of the square. Since points C and D have the same x-coordinate (1) and points A and B also share the same x-coordinate (3), the line of reflection would have to be vertical and equidistant from the x-coordinates of these points. The correct line of reflection is x = 2, which is not listed among the provided options. Therefore, none of the given choices (y = 1, 2x, x = 4, x = 1) correctly maps square ABCD onto itself.