P (Combined system): Rainwater from roofs enters the sewer with sewage; remaining storm water flows separately. Corresponds to P–2.
Q (Vacuum sewer system): Negative pressure in the sewer draws sewage and air from various sources. A pump moves waste from residences to the low-pressure sewer line. Corresponds to Q–4.
R (Partially separate system): Sewage from buildings is channeled through one set of sewers, and storm water through a separate network. Corresponds to R–1.
S (Pressurized sewer system): A pump transfers waste from residences to the low-pressure sewer line. Corresponds to S–3.The correct matching is (A) P–2, Q–4, R–1, S–3.