Select the set of letters that when sequentially placed in the blanks of the given letter series will complete the series. p_rsqrps_pqs_qr_qrps_p_s

q, r, p, s, r, q q, r, p, p, r, q p, r, p, s, r, p r, p, q, s, r, q

q, r, p, s, r, q

p q r s / q r p s / r p q s / p q r s / q r p s / r p q s q , r , p , s , r , q