Final answer:
It can be concluded that AB and CD are both congruent and parallel sides, indicative of a parallelogram, which means options B and C are correct.
Step-by-step explanation:
The information provided suggests that we are dealing with a geometric figure, likely a quadrilateral, where AB is congruent to CD. If AB is congruent to CD and these are opposite sides, this implies that AB and CD have the same length. Congruent sides in a quadrilateral that are also opposite each other usually suggest that these sides are parallel as well. Therefore, it is most reasonable to conclude that the correct answers are both B) a and b are congruent sides and C) c and d are parallel sides.
In a parallelogram, opposite sides are both parallel and congruent. This can be concluded from the fact that AB is congruent to CD, given in the question. If AB and CD are opposite sides of a quadrilateral and they are of equal length, then this quadrilateral must at least be a parallelogram, which by definition has both congruent and parallel opposite sides.