Answer: Choice B. reflection across the y-axis
Reason: Each input x is the opposite as -x.
For instance, x = 2 flips to x = -2
Another example: x = -7 flips to x = 7
Because x flips like this, we have a reflection over the vertical y axis.
The parabola f(x) = x^2 is one example function that makes f(x) = f(-x) true. Notice the symmetry along x = 0.