Friction is reduced by :

Options

A. Ball bearings
B. Glass
C. Both of these
D. None of these

Explanation

### Step-by-Step Solution:

1. **Understanding Friction**: Friction is the resistance that one surface or object encounters when moving over another. It can be reduced by using smoother surfaces or by employing mechanisms that minimize contact.

2. **Identifying Options**: The options provided are:
- Ball bearing
- Glass
- Both of these
- None of these

3. **Analyzing Glass**:
- Glass is a smooth surface, which means that it can reduce friction compared to rough surfaces. However, it does not actively reduce friction; it simply has lower friction compared to other materials.

4. **Understanding Ball Bearings**:
- Ball bearings are mechanical devices that consist of small balls placed between two surfaces. They allow for smooth rotation and movement by reducing the contact area between the moving parts.
- When oil or grease is applied, it further reduces friction between the surfaces, allowing for easier movement.

5. **Conclusion**:
- While glass can reduce friction, it does not actively work to reduce it like ball bearings do. Therefore, the most effective answer to the question "Friction is reduced by" is **ball bearing**.

### Final Answer:
Friction is reduced by **ball bearing**.

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