**Answer:**

The correct answer is option C: 1971.

**Explanation:**

The SI (International System of Units) system was developed and recommended by the General Conference on Weights and Measures (CGPM) in the year 1971. The CGPM is an international organization responsible for maintaining and promoting the SI system.

**Development of the SI system:**

The SI system was developed as a result of ongoing efforts to standardize units of measurement across different countries. The need for a common system of units became more pronounced with the advancement of international trade and scientific collaboration.

The development of the SI system can be traced back to the French Revolution in the late 18th century when the French Academy of Sciences proposed the adoption of a decimal-based metric system. This system became known as the metric system.

Over the years, the metric system underwent several revisions and improvements. In 1960, the 11th CGPM adopted the International System of Units (SI) as the modernized version of the metric system. The SI system provided a comprehensive and coherent framework for measuring physical quantities.

**Recommendation of the SI system:**

The General Conference on Weights and Measures (CGPM) is the international body responsible for overseeing the SI system. It consists of delegates from member countries and convenes once every four years to discuss and make decisions related to the SI system.

In 1971, the 14th CGPM held in Paris recommended the adoption of the SI system as the international standard for units of measurement. This recommendation was based on the recognition of the SI system's advantages in terms of simplicity, uniformity, and compatibility with scientific and technological advancements.

Since then, the SI system has been widely adopted by countries around the world, with the goal of promoting consistency and accuracy in scientific, industrial, and commercial measurements.

In conclusion, the SI system was developed and recommended by the General Conference on Weights and Measures in 1971 as the international standard for units of measurement.