**Core Concept**
The Infant Mortality Rate (IMR) is a widely accepted indicator of a country's overall health and well-being. It is defined as the number of deaths per 1,000 live births of infants under one year of age. The relationship between IMR and socio-economic status (SES) is well-established, with lower SES often correlating with higher IMR.

**Why the Correct Answer is Right**
The correlation between IMR and SES is largely due to the fact that lower SES is associated with poorer access to healthcare, inadequate nutrition, and suboptimal living conditions. These factors contribute to a higher risk of infant mortality, particularly from preventable causes such as infections and congenital anomalies. In addition, lower SES is often linked to higher rates of maternal malnutrition, smoking, and substance abuse during pregnancy, which can further increase the risk of infant mortality.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it oversimplifies the complex relationship between IMR and SES. While there is a correlation, it is not a perfect linear relationship and is influenced by many other factors.

**Option B:** This option is incorrect because it suggests that IMR is solely determined by SES, which is not the case. Other factors such as access to healthcare, maternal education, and environmental conditions also play a significant role.

**Option C:** This option is incorrect because it implies that SES has no impact on IMR, which is not supported by the evidence.

**Clinical Pearl / High-Yield Fact**
A key factor to remember is that IMR is a sensitive indicator of the overall health and well-being of a population, and changes in IMR can reflect improvements or declines in healthcare access and quality.

**Correct Answer: D. It is a complex correlation influenced by multiple factors including access to healthcare, maternal nutrition, and environmental conditions.**