The correct statement that is true for all trapezoids is:

A. one pair of sides are parallel

Here's why the other statements are not true for all trapezoids:

B. Base angles are congruent: This is only true for isosceles trapezoids, not for all trapezoids.

C. Two opposite sides are parallel: This is true for parallelograms, not trapezoids. Trapezoids have exactly one pair of parallel sides.

D. All the angles are congruent: This is not true for any trapezoid. In fact, a trapezoid with all angles congruent would be a rectangle or square, which is a specific type of parallelogram.

Would you like any details or have any questions?

Questions to expand understanding:

1. What are the different types of trapezoids?
2. How can you identify an isosceles trapezoid?
3. What are the properties of parallelograms compared to trapezoids?
4. How do you calculate the area of a trapezoid?
5. What role do the non-parallel sides (legs) play in an isosceles trapezoid?
6. What are the properties of the diagonals in trapezoids?
7. How can you use the midsegment of a trapezoid in solving problems?
8. What are the criteria for a quadrilateral to be classified as a trapezoid?

Tip:

Remember that a trapezoid's defining characteristic is exactly one pair of parallel sides. This key feature distinguishes trapezoids from other quadrilaterals.