The line of reflection is obviously a horizontal line. The only horizontal line in the answer list is ...
A. y = -2
Often, it's not about knowing how to work the problem. It's about being able to eliminate bogus answers and recognizing the form the answer must have.
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You can find points on the line of reflection by finding the midpoint between corresponding vertices. Those midpoints are (-4, -2), (-3, -2), and (-1, -2). The line through all three of those points is y = -2.
