The contractile vacuoles in Paramecium are used mainly for the :
(a) control of body fluid
(b) storage of water
(c) elimination of nitrogenous wastes
(d) elimination of carbon dioxide and ammonia

Options

A. control of body fluid
B. storage of water
C. elimination of nitrogenous wastes
D. elimination of carbon dioxide and ammonia

Explanation

To solve the question regarding the function of contractile vacuoles in Paramecium, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Contractile Vacuoles**:
- Contractile vacuoles are specialized structures found in certain protozoans, including Paramecium. They are membrane-bound organelles that play a crucial role in maintaining cellular homeostasis.

2. **Habitat of Paramecium**:
- Paramecium primarily lives in freshwater environments. This habitat is significant because it influences the osmotic balance of the organism.

3. **Osmoregulation**:
- In freshwater, the concentration of solutes (like salts) outside the Paramecium is lower than inside the cell. This creates a situation where water tends to flow into the cell due to osmosis, potentially leading to swelling and bursting of the cell.

4. **Function of Contractile Vacuoles**:
- The main function of the contractile vacuole in Paramecium is to expel excess water that enters the cell. This process is crucial for osmoregulation, which is the control of the internal water balance and solute concentration.

5. **Evaluating the Options**:
- (a) Control of body fluid: This is correct as it relates to osmoregulation.
- (b) Storage of water: This is incorrect; the vacuole does not store water but expels it.
- (c) Elimination of nitrogenous wastes: This is not the primary function of the contractile vacuole.
- (d) Elimination of carbon dioxide and ammonia: This is also not the primary function of the contractile vacuole.

6. **Conclusion**:
- Based on the analysis, the correct answer is (a) control of body fluid, as the contractile vacuoles help maintain osmotic pressure and regulate the internal fluid balance in Paramecium.

### Final Answer:
(a) control of body fluid