d) All of these
Open drain systems are a breeding place for different flies, mosquitoes, and other disease causing organisms. The waste drainage system should be closed.An open-drain is mostly used to collect wastewater that is not sewage. Use of open drains to dispose of sanitary waste is extremely unhygienic and unsafe. Use of open drains to a certain degree can be acceptable. However, any place with a collection of water breeds various disease-carrying pathogens. Use of open drains is not a good option to carry wastewater even if the solids have been removed by the use of septic or interceptor tanks because people can easily come into contact with it.