**Core Concept**
Ewing's postulates are a set of criteria used to establish the causative relationship between a microorganism and a disease. This concept is crucial in the field of microbiology, where the identification of the causative agent is essential for effective treatment and prevention of disease.

**Why the Correct Answer is Right**
The correct answer is not provided, but Ewing's postulates are used to establish a cause-and-effect relationship between a microorganism and a disease. To fulfill these postulates, the following criteria must be met:
- The microorganism must be found in all individuals with the disease.
- The microorganism must be isolated from the diseased individual and grown in a pure culture.
- The cultured microorganism should cause the disease when introduced into a healthy individual or a laboratory animal.
- The microorganism must be isolated from the healthy individual and grown in a pure culture.
- The cultured microorganism should not cause the disease when introduced into a healthy individual or a laboratory animal.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not provide a clear description of Ewing's postulates.
**Option B:** This option is incorrect because it may refer to other criteria or concepts in microbiology.
**Option C:** This option is incorrect because it may refer to other criteria or concepts in microbiology.

**Clinical Pearl / High-Yield Fact**
Ewing's postulates are a fundamental concept in microbiology, and understanding them is crucial for establishing the causative relationship between a microorganism and a disease.

**Correct Answer:** D.