The answer to this is B. The trap seal is also referred to as the sink trap. This is something that can commonly be found in sinks. The shape of the seal is ideal so that it will be able to retain a certain amount of water depending on how often it is used.
The water will ensure that it will not be possible for the gas coming from the sewage to pass to the drain pipes and go back to the building. This can be very toxic for those who will be affected. It is important to know the proper measurements to make sure that the sink trap will do exactly what it is meant to do.