∆ABC was transformed according to the rule (x, y) → (−x, y) to create ∆A'B'C'. What transformation justifies the relationship between the triangles?

A translation 1 unit to the left and 1 unit upward justifies ∆ABC ~ ∆A'B'C'.
A reflection over the y-axis justifies ∆ABC ≅ ∆A'B'C'.
A rotation of 90° clockwise justifies ∆ABC ~ ∆A'B'C'.
A rotation of 90° counterclockwise justifies ∆ABC ≅ ∆A'B'C'.