Answer: option a. y-axis, x-axis, y-axis, x-axis.
Justification:
1) start with an hypothetical point with general coordinates (a,b)
2) reflecting (a,b) over the y-axis translates it to (-a,b)
3) reflecting (-a,b) over the x-axis translates it to (-a,-b)
4) reflecting (-a,-b) over the y-axis translates it to (a,-b)
5) reflecting (a,-b) over the x-axis translated it to (a,b).
We have proven that that set of reflections carry any point onto itself and so the triangle ABC onto itself.
