Ok the statement right after the blank gives that "angles BCA and DAC are congruent by the same reasoning." These angles appear to me to be congruent according to the alternative interior angles theorem.
Where the parallel lines are BC and AD
after drawing the diagonal, you have 2 pairs of alternate angles in parallel lines... one pair has been identified, you need to identify the other pair |dw:1444072264928:dw| the equal angles are marked, the proof is Angle - Side -Angle...
Therefore the answer looks to be D, that angles BAC DCA are congruent by the same theorem where the parallel lines are taken to be CD and AB
Alternative Interior Angles Theorem gives that parallel lines cut by a transversal will yield 4 (interior) angles where the opposite angles are equal to one another as campbell shows.. here is something to get a little background: http://hotmath.com/hotmath_help/topics/alternate-interior-angles-theorem.html
the easy think to do in this question is sketch the diagram, do the construction, mark which is given to you and work from there... Open study is about helping understanding and not doing people's homework