**Core Concept**
The Sample Registration System (SRS) is a dual-record system used for estimating demographic indicators such as birth and death rates, fertility, and population growth. It involves a continuous enumeration of births and deaths by an enumerator, while a surveyor visits the area every six months to record the events and collect information on a sample of ever-married women.

**Why the Correct Answer is Right**
The SRS combines the strengths of both continuous enumeration and interval surveys to provide accurate and reliable estimates of demographic indicators. The continuous enumeration by the enumerator ensures that all events are recorded, while the surveyor's visits provide a check on the accuracy of the data and collect information on a sample of ever-married women to estimate fertility and other indicators. The SRS is considered a gold standard for demographic estimation.

**Why Each Wrong Option is Incorrect**
**Option A:** The SRS is not a census, as it involves a sample of the population rather than a complete enumeration.
**Option B:** The SRS is not a survey of ever-married women only, although it does collect information on a sample of these women to estimate fertility and other indicators.
**Option C:** The SRS is not a one-time survey, as it involves continuous enumeration by the enumerator and interval surveys by the surveyor.

**Clinical Pearl / High-Yield Fact**
The SRS is an example of a dual-record system, which is a method of data collection that combines the strengths of different data collection methods to provide accurate and reliable estimates.

**Correct Answer: C. The Sample Registration System is not a one-time survey, as it involves continuous enumeration by the enumerator and interval surveys by the surveyor.