Which of the following sets of conditions is sufficient to conclude that four distinct points P,Q,R,S are concyclic?
(a) ∠PQS=∠PRS and both angles are on opposite sides of PS
(b) ∠PSQ=∠PRQ and both angles are on the same side of PQ
(c) PQ=QR and QR=RS
(d) ∠PQS+∠QRS=180∘