First, let's look at the properties of the quadrilaterals mentioned in your question.
Trapezoids - quadrilateral with exactly one pair of parallel sides (called bases)
Rectangle - a parallelogram (two pairs of parallel sides) with four right angles
Square - a parallelogram with four right angles and four congruent sides
Shawndra said that it's not possible to draw a trapezoid that is a rectangle. She is correct. A rectangle contains 2 pairs of parallel sides and trapezoids only have one pair of parallel sides.
Shawndra then said that she can draw a square that is a rectangle. Every square is a rectangle because all squares have four right angles and two pairs of parallel sides.
Marcella said that both are possible. From looking at the properties above, we can see that Shawndra is correct.
