Protozoan found commensal in human colon is

Options

A. Entamoeba coli
B. P. vivax
C. A. aegypti
D. All the above.

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks for a protozoan that is found as a commensal in the human colon. This means we need to identify a protozoan that benefits from living in the human colon without harming the host.

2. **Defining Commensalism**: Commensalism is a type of symbiotic relationship where one organism benefits while the other is neither helped nor harmed. In this context, we are looking for a protozoan that fits this definition.

3. **Analyzing the Options**:
- **Option 1: Entamoeba coli**: This is a protozoan that is known to inhabit the human colon and is considered a commensal organism. It derives nutrients from the host but does not cause harm.
- **Option 2: P. vivax**: This refers to Plasmodium vivax, which is a protozoan that causes malaria. This organism is parasitic, meaning it harms the host, so it does not fit the definition of a commensal.
- **Option 3: A. aegypti**: This is actually a mosquito (not a protozoan) and is known to be a vector for diseases like dengue fever. It does not fit the criteria of a commensal protozoan.
- **Option 4: All of the above**: Since only Entamoeba coli is a commensal protozoan, this option is incorrect.

4. **Conclusion**: Based on the analysis, the correct answer is **Entamoeba coli**, as it is the only organism listed that is a protozoan and acts as a commensal in the human colon.

### Final Answer:
**Entamoeba coli**