During "elastic collision"
a) there is no loss of kinetic energy
b) the bodies are perfectly elastic
c) temporarily some of the kinetic energy is used to deform the bodies
d) after collision the bodies regain the original shape keeping the total energy constant

Options

A. only "a" is true
B. a,b,c,d are true
C. b,c,d are true
D. a,b,c are true

Explanation

To solve the question regarding elastic collisions, we need to analyze each option provided and determine their validity based on the principles of physics.

### Step-by-Step Solution:

1. **Understanding Elastic Collision**:
- An elastic collision is defined as a collision where both momentum and kinetic energy are conserved. This means that the total kinetic energy before and after the collision remains the same.

2. **Analyzing Option (a)**:
- **Statement**: "There is no loss of kinetic energy."
- **Evaluation**: This statement is true. In elastic collisions, the kinetic energy before the collision is equal to the kinetic energy after the collision.

3. **Analyzing Option (b)**:
- **Statement**: "The bodies are perfectly elastic."
- **Evaluation**: This statement is also true. In an elastic collision, the colliding bodies are considered to be perfectly elastic, meaning they can deform and return to their original shape without any loss of energy.

4. **Analyzing Option (c)**:
- **Statement**: "Temporarily some of the kinetic energy is used to deform the bodies."
- **Evaluation**: This statement is true as well. During the collision, the kinetic energy is temporarily converted into potential energy as the bodies deform. However, they regain this energy as they return to their original shape.

5. **Analyzing Option (d)**:
- **Statement**: "After collision the bodies regain the original shape keeping the total energy constant."
- **Evaluation**: This statement is true. After the collision, the bodies do return to their original shape, and the total mechanical energy (kinetic + potential) remains constant throughout the process.

### Conclusion:
Since all four statements (a, b, c, and d) are true regarding elastic collisions, the correct answer is that all options are correct.

### Final Answer:
**All options (a, b, c, d) are correct.**

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