Which figure is a counterexample to the following statement? a quadrilateral with one pair of parallel sides is a parallelogram. a. a right triangle has perpendicular sides. b. a square is a rectangle. c. a dart is not a parallelogram. d. a trapezoid is not a parallelogram.

The correct option is D.

Option A. isn't even about quadrilater, so we can immediately discard it.

Option B. statement is true, but has nothing to do with the point of the question. In fact, it is true that every square is in particular a rectangle, but in turn every rectangle is a parallelogram. So, there's no counterexample here

Option C. is false, because a dart is a parallelogram: both of its opposite sides are parallel.

Option D. finally presents a counterexample. In fact, The two bases of a trapezoid are parallel, but the two other sides are not. So, a trapezoid is not a parallelogram, even though it has a pair of parallel sides. This is way, in order to be a parallelogram, it is necessary for the quadrilateral to have two pairs of parallel sides.