**Core Concept**
The question is testing knowledge of public health and sanitation principles. An effective sewage disposal method for a small community involves treating and safely disposing of wastewater to prevent waterborne diseases.

**Why the Correct Answer is Right**
The correct answer is septic tank with soak pits. A septic tank is a cost-effective and efficient method for treating sewage in a small community. It involves the use of a septic tank to break down organic matter and a soak pit to filter and disinfect the effluent. The septic tank's anaerobic environment allows for the breakdown of organic matter, while the soak pit provides a large surface area for filtration and disinfection.

**Why Each Wrong Option is Incorrect**
**Option A:** Landfills are not suitable for sewage disposal as they do not treat the wastewater and can lead to environmental pollution.
**Option B:** Incineration is a method of waste disposal, but it is not suitable for sewage disposal as it does not treat the wastewater and can release toxic gases.
**Option C:** Sewage treatment plants are effective for large communities, but they are expensive and not feasible for small communities.

**Clinical Pearl / High-Yield Fact**
In public health, the goal is to prevent waterborne diseases by ensuring proper sewage disposal. A septic tank with soak pits is an effective and cost-efficient method for small communities.

**Correct Answer:** C.