A trapezium is a quadrilateral with at least one pair of parallel sides. A quadrilateral has vertices, taken in order, at A(1, 1), B(9, 1), C(7, 5) and D(3, 5). Which description fits it best?

AB runs along $y=1$ with length 8, and DC runs along $y=5$ with length 4, so AB and DC are parallel — one pair of parallel sides, which satisfies the definition. They are unequal, so it is not a parallelogram. The other two sides are AD = √$(2^2+4^2)=$ √20 and BC = √$((-2{)}^2+4^2)$ = √20, equal to each other, so the trapezium is isosceles. It is not a kite, since a kite has two pairs of equal adjacent sides.