Select the correct statement about skeletal system in some animals.

Options

A. Earthworms have liquid skeleton i.e., the liquid trapped in body spaces keeps the body firm.
B. Sharks have skeleton present outside their body only and not inside.
C. Snakes and birds have hollow bones which reduce their body weight and make the movement easier.
D. Cockroaches have an endoskeleton made of chitin.

Explanation

To solve the question about selecting the correct statement regarding the skeletal system in some animals, we will analyze each of the four statements provided.

### Step-by-Step Solution:

1. **Read Statement A**: "Earthworms have a liquid skeleton, i.e., the liquid trapped in the body surfaces keeps the body firm."
- **Analysis**: This statement is correct. Earthworms do have a hydrostatic skeleton, which is a liquid-filled cavity that helps maintain their shape and provides support.

2. **Read Statement B**: "Sharks have skeleton present outside their body only and not inside."
- **Analysis**: This statement is incorrect. Sharks have a skeleton made of cartilage, which is present both inside and provides some external structure.

3. **Read Statement C**: "Snakes and birds have hollow bones which reduce their body weight and make the movement easier."
- **Analysis**: This statement is incorrect. While birds have hollow bones to reduce weight for flight, snakes do not have hollow bones; they have solid bones.

4. **Read Statement D**: "Cockroaches have an endoskeleton made of chitin."
- **Analysis**: This statement is incorrect. Cockroaches have an exoskeleton made of chitin, not an endoskeleton.

### Conclusion:
After analyzing all the statements, the correct statement is **Statement A**: "Earthworms have a liquid skeleton, i.e., the liquid trapped in the body surfaces keeps the body firm."

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