Consider that trapezoid is a type of quadrilateral, which has one pair of opposite sides unequal but parallel, and the other pair of opposite sides are non-parallel.
Now, read the options carefully. We have to mark the option that is always true for a trapezoid.
Option A:
It is not necessary for a trapezoid to have both pairs of opposite sides as parallel. Only one pair being parallel is required for a quadrilateral to be a trapezoid.
Option B:
As discussed above, the statement is correct for every trapezoid.
Option C:
This is not a necessary condition for a trapezoid. There exist some trapezoids that don't have the opposite angles congruent.
Option D:
Again, this is not a necessary condition for a trapezoid. Since one pair of sides is non-parallel, the other pair must be unequal.
Therefore, it can be concluded that option B is the correct choice.