The answer depends on the definition of trapezoid. There are two valid definitions of a trapezoid. Find out the one your teacher uses, and answer accordingly.
1) Definition: A trapezoid is a quadrilateral with exactly one pair of opposite sides parallel.
According to this definition, a trapezoid has one pair of opposite sides parallel and one pair of opposite sides that is not parallel. According to this definition, a quadrilateral cannot be both a trapezoid and a parallelogram.
Answer: 1 pair
2) Definition: A trapezoid is a quadrilateral with at least one pair of opposite sides parallel.
According to this definition, if at least one pair of opposite sides is parallel, the quadrilateral is a trapezoid. If both pairs of opposite sides are parallel, then it is still a trapezoid, but now it is also a parallelogram. According to this definition, a parallelogram is a special case of a trapezoid.
Answer: 1 pair or 2 pairs
