**Core Concept**
The General Fertility Rate (GFR) is a demographic measure that estimates the number of births per 1,000 women of reproductive age in a given population. It is an essential indicator of fertility trends and is used to assess the reproductive health of a population.

**Why the Correct Answer is Right**
The correct denominator for the General Fertility Rate is the number of women in the reproductive age group (usually defined as 15-44 years) in a given year. This is because the GFR is intended to capture the number of births that occur within this age group, which is the most fertile period in a woman's life. By using the number of women in this age group as the denominator, the GFR provides a standardized measure of fertility that can be compared across different populations and time periods.

**Why Each Wrong Option is Incorrect**
**Option A:** Married women in reproductive age group in a given year - This option is incorrect because the GFR is intended to capture the fertility of all women in the reproductive age group, regardless of their marital status.

**Option C:** Married women in any specified age group - This option is incorrect because the GFR is focused on the reproductive age group (15-44 years), not any specified age group.

**Option D:** Women in any specified age group - This option is incorrect because the GFR is specifically designed to capture the fertility of women in the reproductive age group, not women of any age.

**Clinical Pearl / High-Yield Fact**
When calculating the General Fertility Rate, it's essential to use the number of women in the reproductive age group as the denominator, as this provides a standardized measure of fertility that can be compared across different populations and time periods.

**Correct Answer Line**
✓ Correct Answer: B. Women in reproductive age group in a given year