**Core Concept**
The iodine deficiency control program aims to prevent iodine deficiency disorders (IDD) by ensuring adequate iodine intake through the diet. Iodine is essential for thyroid hormone production, and deficiency can lead to goiter, hypothyroidism, and cretinism. The program focuses on fortifying a commonly consumed food item with iodine to reach the target population.

**Why the Correct Answer is Right**
The correct answer, "Fortification of salt," is the most effective method to control iodine deficiency. Salt is a staple in most households and consumed by people of all ages, making it an ideal vehicle for iodine fortification. The process involves adding iodine to salt during the manufacturing process, ensuring that every household has access to iodized salt. This approach has been successful in countries like the United States, where iodine deficiency was once a significant public health concern. The iodine fortification program has been implemented in many countries, including India, to combat IDD.

**Why Each Wrong Option is Incorrect**
**Option A:** Health education is an essential component of public health programs, but it is not the primary method for controlling iodine deficiency. While awareness about the importance of iodine is crucial, it is not a substitute for iodine fortification.

**Option B:** Water testing is not a direct method for controlling iodine deficiency. Although iodine can be added to water, it is not a practical or cost-effective solution for widespread iodine fortification.

**Option D:** "None" is incorrect because one of the options listed is indeed a correct method for controlling iodine deficiency.

**Clinical Pearl / High-Yield Fact**
In areas with high iodine deficiency, goiter can be a significant public health concern. Goiter is characterized by an enlarged thyroid gland, which can lead to respiratory problems and other complications. The iodine fortification program has been instrumental in reducing goiter prevalence in many countries.

**✓ Correct Answer: C. Fortification of salt**