The correct answer is: A. Separate system.
A separate system is a type of sanitation system that separates sewage from storm water. This is the most common type of sanitation system in the United States. It is suitable for areas of distributed rainfall throughout the year with less intensity because it can handle the smaller amounts of runoff that occur during these types of storms.
A combined system is a type of sanitation system that collects both sewage and storm water in the same pipe. This type of system is less common in the United States, but it is more common in Europe and Asia. It is not suitable for areas of distributed rainfall throughout the year with less intensity because it can overload the system during heavy rains.
A partially separate system is a type of sanitation system that collects sewage and storm water in separate pipes, but the storm water pipe is connected to a treatment plant. This type of system is less common than a separate system or a combined system. It is not suitable for areas of distributed rainfall throughout the year with less intensity because it can overload the treatment plant during heavy rains.
A partially combined system is a type of sanitation system that collects sewage and storm water in the same pipe, but the storm water pipe is only connected to a treatment plant during heavy rains. This type of system is the least common type of sanitation system. It is not suitable for areas of distributed rainfall throughout the year with less intensity because it can overload the treatment plant during heavy rains.