## Core Concept
The term "eligible couple" refers to a specific definition in the context of family planning and reproductive health. It is essential to understand the demographic and health indicators used to assess the needs and status of populations.

## Why the Correct Answer is Right
The correct definition of an "eligible couple" is a married couple in the reproductive age group, typically defined as 15-49 years, where the wife is in the reproductive age group. This definition is crucial for family planning programs and demographic studies.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because it does not accurately represent the definition of an eligible couple.
- **Option B:** This option is incorrect because it does not specify the age range or marital status accurately.
- **Option C:**
- **Option D:** This option is incorrect because it does not accurately define an eligible couple.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the definition of an eligible couple is vital for assessing the needs for family planning services and understanding population dynamics. The typical age range considered for eligible couples is 15-49 years for the wife.

## Correct Answer: D. Married couple with wife in reproductive age group.