**Core Concept**
Human Development Index (HDI) is a composite statistic of life expectancy, education, and per capita income indicators, which are used to rank countries into four tiers of human development. The HDI is a widely used metric to assess a country's overall development and well-being.

**Why the Correct Answer is Right**
The HDI was first introduced by the United Nations Development Programme (UNDP) in 1990 as a measure to complement the Gross National Product (GNP) in evaluating a country's development. The HDI has undergone revisions over the years to improve its methodology and accuracy. The correct answer refers to the year when the HDI was first introduced or revised. The UNDP released the first Human Development Report in 1990, the second report in 1991, and subsequent reports in the following years.

**Why Each Wrong Option is Incorrect**
**Option A:** March 2009 - This is not a significant date for the introduction or revision of the HDI.
**Option B:** September 2009 - This is also not a significant date for the HDI.
**Option C:** September 2012 - This is not a significant date for the HDI.
**Option D:** March 2013 - This is not a significant date for the HDI.

**Clinical Pearl / High-Yield Fact**
One important aspect of the HDI is that it is not a direct measure of economic growth, but rather a measure of the quality of life and well-being of a country's citizens. It takes into account factors such as life expectancy, education, and income inequality, which are crucial indicators of a country's development.

**Correct Answer:** A. March 2009.