Answer:
C. the quadrilateral is a square. The parallelogram is both a rhombus and a rectangle.
Explanation:
All parallelograms are quadrilaterals. All rhombuses and rectangles are parallelograms, all squares are both rhombuses and rectangles.
A parallelogram is a rhombus when the diagonals bisect opposite angles.
A parallelogram is a rectangle if the diagonals are congruent to each other.
Since the given parallelogram has the properties of both a rhombus and a rectangle, it is a square. The correct answer is C.
I really hope this helps =)