The length of PQ and RS both depend on the relative position of each point on the circle, which is not given. If P and Q are closer together than R and S are to each other, than RS > PQ. If, on the other hand P and Q are farther apart on the circumference of the circle than R and S are to each other, PQ > RS. Since there’s no way to determine the positions of the points, the answer has to be D.