Quadrilateral abcd underwent a sequence of transformations to give quadrilateral a′b′c′d′. which transformations could not have taken place? a reflection across the line y = x followed by a reflection across the line y = -x a reflection across the x-axis followed by a reflection across the y-axis a rotation 180° clockwise about the origin followed by a reflection across the line y = x or a reflection across the y-axis followed by a reflection across the x-axis