Pick up the incorrect statement regarding a master trap from the following

Q. Pick up the incorrect statement regarding a master trap from the following:

A.            The water seal is less than that of ordinary traps

B.            It is provided a cleaning eye at the top of the trap

C.            It is provided in between the lower end of the house drain and the street sewer

D.            The mica flap valve which opens inwards only, is fitted at the top of the inlet pipe

Answer: The water seal is less than that of ordinary traps