`{:(,"Column A",,,"Column B"),(A.,"Defecation by living being","( )",a.,"Arsenic, mercury etc"),(B.,"Industrial operation","( )",b.,"Intesecticides, fungicides etc"),(C.,"Thermal pollution","( )",c.,"Amoeba, fungicides etc"),(D.,"Agricultural activities","( )",d.,"Favourable for growth of algae"):}`

Explanation

To solve the problem, we need to match the items in Column A with the appropriate items in Column B based on the descriptions provided. Let's analyze each item step by step.

### Step-by-Step Solution:

1. **Identify the first item in Column A: Defecation by living beings.**
- **Explanation:** Defecation refers to the discharge of feces from the body, which can introduce pollutants into the environment.
- **Match:** This process can lead to the introduction of pollutants such as amoeba and fungicides.
- **Conclusion:** A matches with C (Defecation by living beings → Amoeba, fungicides, etc.).

2. **Identify the second item in Column A: Industrial operation.**
- **Explanation:** Industrial operations often result in the release of harmful substances into the environment.
- **Match:** Common pollutants from industrial operations include heavy metals like arsenic and mercury.
- **Conclusion:** B matches with A (Industrial operation → Arsenic, mercury, etc.).

3. **Identify the third item in Column A: Thermal pollution.**
- **Explanation:** Thermal pollution occurs when water from thermal power plants is released into natural water bodies, raising the temperature of the water.
- **Match:** This increase in temperature can create favorable conditions for the growth of algae.
- **Conclusion:** C matches with D (Thermal pollution → Favourable for growth of algae).

4. **Identify the fourth item in Column A: Agricultural activities.**
- **Explanation:** Agricultural activities often involve the use of pesticides and fertilizers, which can contaminate water bodies.
- **Match:** These activities produce pollutants such as insecticides and fungicides.
- **Conclusion:** D matches with B (Agricultural activities → Insecticides, fungicides, etc.).

### Final Matches:
- A matches with C
- B matches with A
- C matches with D
- D matches with B

### Summary of Matches:
- A (Defecation by living beings) → C (Amoeba, fungicides, etc.)
- B (Industrial operation) → A (Arsenic, mercury, etc.)
- C (Thermal pollution) → D (Favourable for growth of algae)
- D (Agricultural activities) → B (Insecticides, fungicides, etc.)