Question

What must be true of PQ?

Answer 1

Interesting question
Usually when you look at something like that construction, you think that AB has been bisected by PQ and that the two segments are perpendicular. They are perpendicular but nowhere is that stated. So the answer is C because all the other answers are wrong. 

PQ is congruent AB is not correct. As long as the arcs are equal and meet above and below AB there is no proof of congruency. In your mind widen the compass legs so that they are wider than AB and redraw the arcs. You get a larger PQ, but it has all the original properties of PQ except size.

PQ is not congruent to AQ. How would you prove conguency? You'd have to put both lines into triangles that can be proved congruent. It can't be done.

The two lines are not parallel. They are perpendicular. That can be proven. They meet at right angles to each other (also provable).