Hey there! I'm happy to help!
We see that all of our y-values go negative and our x-values stay the same. It isn't a rotation because then our x-values will switch, but they haven't switched in our problem, so A and D are incorrect.
Reflecting over the line y=x is just reflecting over a diagonal line, and that will switch the x-value as well.
The correct answer is B. reflect over the x-axis. All of the x-values stay the same here, but the y-values are all on the other side of the x-axis, so they are all negative now, and this matches the change we see with our points.
Have a wonderful day and keep on learning! :D