Which of the following is not a unit of speed ?

Options

A. `ms^(-1)`
B. `mih^(-1)`
C. `km h^(-1)`
D. `"knot" `h^(-1)`

Answer

To determine which of the following options is not a unit of speed, we will analyze each option provided:

1. **Meter per second (m/s)**:
- This is a standard unit of speed in the International System of Units (SI). It measures how many meters are traveled in one second.
- **Conclusion**: This is a unit of speed.

2. **Mile per hour (mi/h)**:
- This unit measures how many miles are traveled in one hour. It is commonly used in the United States and other countries that use the imperial system.
- **Conclusion**: This is a unit of speed.

3. **Kilometer per hour (km/h)**:
- This unit measures how many kilometers are traveled in one hour. It is widely used for speed limits and vehicle speeds in many countries.
- **Conclusion**: This is a unit of speed.

4. **Knot per hour (not/h)**:
- The term "knot" is a unit of speed that is equal to one nautical mile per hour. However, the term "knot per hour" is not a standard unit of speed; it is redundant because a knot already indicates speed per hour.
- **Conclusion**: This is not a standard unit of speed.

Based on the analysis, the option that is not a unit of speed is **Knot per hour (not/h)**.

### Final Answer:
**Knot per hour (not/h)** is not a unit of speed.

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