Select all transformations that maintain a shape's congruency.
a translation six units up


a reflection across the x-axis


a 180° rotation about the origin


a dilation with a scale factor of 2


a reflection across the y-axis and then a translation three units left


a translation two units down and then a dilation with a scale factor of less than 1


a reflection across the y-axis and then a dilation with a scale factor greater than 1