The first step is to locate the points to find what kind of quadrilateral this is.
The next step is to find the lengths of the diagonals, if both have the same length then the quadrilateral is a rectangle, if the don't the quadrilateral is a parallelogram.
When looking at the picture is easy to determine that the quadrilateral is a parallelogram, but the statement that could prove what kind of quadrilateral this is is C. Find the lengths of the diagonals to show that the quadrilateral is a parallelogram.