A. Is wrong because only some of the parallelograms is similar.
B. Is wrong because all rhombuses are squares but not all squares are rhombuses.
C. Is wrong because rectangles have different sizes even though the angles are congruent.
D. Is correct because all trapezoids are parallelograms but all parallelograms are not 
     trapezoids because parallelograms have two pair of sides congruent while trapezoids
     have only one pair of congruent sides.
so, the correct answer is letter D.
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