In quadrilateral PQRS, sides PS and QR have equal length and sides PQ and RS are parallel to each other. Point X is the intersection of the diagonals PR and QS. Which of the following conclusions must be true?
Type your answer as a list of letters separated by commas. For instance, if you believe that conditions A, B, and C are enough, then type "A,B,C" into the answer box. If you believe none of the options are correct, enter "none."