## Core Concept
Ewing's postulates are criteria used to establish a causal relationship between a microbe and a disease. These postulates are an extension of Koch's postulates and are specifically applied to situations where Koch's postulates cannot be fulfilled, such as in cases of viral infections or when the microorganism cannot be cultured.

## Why the Correct Answer is Right
Ewing's postulates are relevant in the context of molecular and genetic relationships between pathogens and diseases. They emphasize the role of specific genes or gene products of the microorganism in causing disease. This includes demonstrating that the gene or gene product is associated with the pathogenicity of the microorganism and that its presence or expression correlates with the disease phenotype.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because it does not accurately represent Ewing's postulates.
- **Option B:** This option is incorrect because it does not relate to Ewing's postulates.
- **Option C:** This option might relate to other scientific principles or postulates not specifically attributed to Ewing in the context provided.
- **Option D:** This option is incorrect as it does not correctly identify Ewing's postulates.

## Clinical Pearl / High-Yield Fact
A key point to remember is that Ewing's postulates help in understanding the molecular basis of pathogenesis, which is crucial for developing targeted therapies and diagnostic tests. These postulates are particularly useful in identifying virulence factors and understanding the pathogenesis of diseases caused by viruses and other microorganisms that are difficult to culture.

**Correct Answer: D.**