**Core Concept**
Quality assurance (QA) and quality control (QC) are two distinct concepts in healthcare and medical research. Quality assurance refers to the overall management system that ensures quality, whereas quality control is the process of monitoring and evaluating the quality of specific products or services.

**Why the Correct Answer is Right**
Quality control (QC) is a subset of quality assurance (QA). Internal quality assurance (IQA) refers to the processes and systems within an organization that ensure quality, while external quality assurance (EQA) involves independent evaluation of an organization's quality management system by external auditors or experts. The correct answer describes the hierarchical relationship between these concepts: QA > QC, with IQA and EQA being subsets of QA.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not accurately describe the relationship between QA, QC, IQA, and EQA.
**Option B:** This option is incorrect as it inverts the correct hierarchical relationship between QA and QC.
**Option C:** This option is incorrect as it fails to distinguish between internal and external quality assurance.

**Clinical Pearl / High-Yield Fact**
Remember the QA-QC-IQA-EQA hierarchy: Quality Assurance (QA) is the overarching system, with Quality Control (QC) being a subset, and Internal Quality Assurance (IQA) and External Quality Assurance (EQA) being subsets of QA. This hierarchy ensures that quality is maintained and improved throughout an organization.

**Correct Answer:** D.