_______is the first step of sewage treatment.

Options

A. Precipitation
B. Chlorination
C. Sedimentation
D. Aeration

Explanation

**Step-by-Step Solution:**

1. **Understanding Sewage Treatment**: Sewage treatment is a process aimed at removing contaminants from wastewater or sewage to convert it into clean water. This process involves several steps.

2. **Identifying the Steps of Sewage Treatment**: The common steps in sewage treatment include:
- Precipitation
- Chlorination
- Sedimentation
- Aeration

3. **Determining the First Step**: The question specifically asks for the first step in the sewage treatment process. The first step is known as primary treatment.

4. **Describing Primary Treatment**: Primary treatment involves the physical removal of solid particles from sewage. This is achieved through two main processes:
- **Filtration**: This process removes floating debris from the sewage.
- **Sedimentation**: This process allows heavier particles, such as soil and small pebbles (referred to as grit), to settle at the bottom.

5. **Concluding the Answer**: Based on the processes involved in primary treatment, the first step of sewage treatment is **sedimentation**.

**Final Answer**: Sedimentation is the first step of sewage treatment.

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