Select all transformations that maintain a shape's congruency.
A: a translation six units up
B: a reflection across the x-axis
C: a 180° rotation about the origin
D: a dilation with a scale factor of 2
E: a reflection across the y-axis and then a translation three units left
F: a translation two units down and then a dilation with a scale factor of less than 1
G: a reflection across the y-axis and then a dilation with a scale factor greater than 1