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