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