Which sequence is not equivalent to the others?

a. a reflection across the y-axis, followed by a reflection across the x-axis, and then a 90° clockwise rotation about the origin
b. a 90° clockwise rotation about the origin and then a 180° rotation about the origin
c. a reflection across the x-axis, followed by a 90° counterclockwise rotation about the origin, and then a reflection across the x-axis
d. a 90° counterclockwise rotation about the origin