If no gaskets are used in the piping joints of a Freon system, the joints must be（）

A.a clogged scale trap
B.air in the system
C.automatic controls not functioning properly
D.insufficient cooling water to the condenser

A.separating chamber
B.system of baffles
C.purge valve
D.vacuum reducing valve

A.saltwater side of the condenser
B.refrigerant side of the condenser
C.in the evaporator coils
D.in the suction strainer