## **Core Concept**
The Sample Registration System (SRS) is a dual-record system used in India to estimate vital statistics, particularly birth and death rates. It is a critical tool for monitoring population health and demographic changes.

## **Why the Correct Answer is Right**
The SRS involves continuous enumeration of births and deaths by a resident part-time enumerator, with an independent 6-monthly retrospective survey by a supervisor. This system is conducted **every 6 months** to ensure accurate and up-to-date vital statistics. The correct answer reflects the frequency of the SRS survey.

## **Why Each Wrong Option is Incorrect**
- **Option A (1 month):** This is too frequent for the SRS survey, which is designed to be conducted at intervals that balance accuracy with practicality.
- **Option B (1 year):** This is less frequent than the actual survey interval, which could lead to outdated statistics and reduced accuracy in tracking vital events.
- **Option D (2 years):** This is even less frequent than option B and would likely result in significant underreporting and outdated data.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the Sample Registration System is crucial for **epidemiological studies** and **health program evaluations** in India. Its dual-record system enhances the accuracy of vital statistics, making it a valuable tool for public health planning.

## **Correct Answer:** C. 6 months.