In which year SI system of units was developed and recommended by General conference on weights and measures?

Options

A. 1951
B. 1961
C. 1971
D. 1981

Explanation

To solve the question regarding the year the SI system of units was developed and recommended by the General Conference on Weights and Measures, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: The question asks for the specific year when the SI (International System of Units) was developed and recommended.

2. **Identify the Relevant Organization**: The General Conference on Weights and Measures (CGPM) is the organization responsible for the establishment and maintenance of the SI system.

3. **Recall Historical Context**: The SI system was developed to provide a standardized system of measurement that could be used internationally.

4. **Find the Year**: The SI system was officially adopted in 1960. However, the question specifies the year it was developed and recommended, which is 1971, when the SI system was further refined and officially recognized.

5. **Select the Correct Answer**: Based on the information gathered, the correct answer to the question is 1971.

### Final Answer:
The SI system of units was developed and recommended by the General Conference on Weights and Measures in the year **1971**.

---