The correct answer is D. All of the above.
The water carriage system of collection of waste products is a system in which waste products are flushed away with water and transported through pipes to a treatment plant. This system is more expensive to install than dry conservancy systems, but it is more hygienic and does not create the same problems with odor and pests. However, it does require treatment before disposal, as the wastewater can contain harmful bacteria and viruses.
Dry conservancy systems, on the other hand, are less expensive to install but they are not as hygienic. Waste products are collected in a bucket or other container and must be disposed of regularly. This can create problems with odor and pests, and it can also be a health hazard if the waste is not disposed of properly.
Ultimately, the best system for a particular community will depend on a number of factors, including cost, availability of water, and the level of sanitation that is desired.