Which set of transformations proves that rectangle ABCD is congruent to rectangle A'B'C'D'?
A.a translation of rectangle ABCD 7 units to the left, followed by a translation 7 units down
B.a reflection of rectangle ABCD across the x-axis, followed by a reflection across the y-axis
C.a reflection of rectangle ABCD across the y-axis, followed by a translation 7 units down
D.a 180° rotation of rectangle ABCD about the origin, followed by a translation 3 units up