Which of the following system of units is not based on units of mass, length and time alone

Options

A. CGS
B. FPS
C. MKS
D. SI

Explanation

To determine which system of units is not based solely on mass, length, and time, we will analyze the given options: CGS, FPS, MKS, and SI.

### Step-by-Step Solution:

1. **Understanding the Systems of Units**:
- **CGS (Centimeter-Gram-Second)**: This system uses the centimeter for length, gram for mass, and second for time. It is based on the three fundamental dimensions of mass, length, and time.
- **FPS (Foot-Pound-Second)**: This system uses the foot for length, pound for mass, and second for time. Like CGS, it is also based on mass, length, and time.
- **MKS (Meter-Kilogram-Second)**: This system uses the meter for length, kilogram for mass, and second for time. It is again based on the three fundamental dimensions of mass, length, and time.
- **SI (International System of Units)**: This system is more comprehensive and is based on seven fundamental units, which include mass (kilogram), length (meter), time (second), temperature (kelvin), luminous intensity (candela), amount of substance (mole), and electric current (ampere).

2. **Identifying the Unique System**:
- From the analysis, we can see that CGS, FPS, and MKS are all based solely on mass, length, and time.
- However, the SI system includes additional fundamental units beyond just mass, length, and time.

3. **Conclusion**:
- Therefore, the system of units that is not based solely on mass, length, and time is **SI**.

### Final Answer:
The correct answer is **SI** (Option D).