Triangle ABC underwent a sequence of transformations to give triangle A′B′C′. Which transformations could not have taken place? A. a reflection across the line y = x followed by a reflection across the line y = -x B. a reflection across the x-axis followed by a reflection across the y-axis C. a rotation 180° clockwise about the origin followed by a reflection across the line y = x D. a reflection across the y-axis followed by a reflection across the x-axis