**Core Concept**
Nutrition surveillance refers to the systematic collection, analysis, and interpretation of data to monitor and evaluate the nutritional status of populations, enabling informed decision-making for public health interventions. This involves understanding the nutritional trends, patterns, and determinants of a population, which is essential for designing effective nutrition programs.

**Why the Correct Answer is Right**
Nutrition surveillance typically involves the collection of data from various sources, including census data, which provides baseline information on the population's demographic characteristics. Additionally, census data can be used to identify areas with high levels of poverty, malnutrition, or other social determinants that may impact nutrition. Policy makers use this information to develop evidence-based policies and interventions to improve nutrition outcomes.

**Why Each Wrong Option is Incorrect**
* **Option A:** Policy makers are not a component of nutrition surveillance, but rather a group that uses the data collected through surveillance to inform their decisions.
* **Option B:** Nutritional survey is a method used to collect data, but it is not a component of nutrition surveillance.
* **Option C:** Census is indeed a component of nutrition surveillance, as it provides valuable demographic data that can be used to inform nutrition interventions.
* **Option D:** Low birth rate is a potential outcome of poor nutrition, but it is not a component of nutrition surveillance.

**Clinical Pearl / High-Yield Fact**
To remember the components of nutrition surveillance, think of the "3 Cs": Census, Community-based surveys, and Clinical data. These data sources provide the foundation for understanding the nutritional status of populations and informing effective public health interventions.

**Correct Answer:** C. Census.