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