From the question given, we are asked to determine the missing steps to prove that QUAD is a parallelogram.
recall, for a diagram to be a parallelogram, the slope of the vertices must be equal.
So, the missing step is:
line QU is parallel to line AD and line UA is parallel to line DQ because the segments have the same slope.
Therefore, the correct option is A, which is line QU is parallel to line AD and line UA is parallel to line DQ because the segments have the same slope.