**Core Concept**
The Physical Quality of Life Index (PQLI) is a composite measure of health, literacy, and infant mortality that aims to quantify the quality of life in a country. It takes into account three key indicators: literacy rate, infant mortality rate, and life expectancy at age one.

**Why the Correct Answer is Right**
The PQLI is a widely used index to evaluate the overall well-being of a population. It is calculated based on the following formula: PQLI = (2/3) Literacy Rate + (1/3) Infant Mortality Rate + (1/3) Life Expectancy at Age One. The PQLI scores are then used to rank countries in terms of their quality of life. The inclusion of these three indicators provides a comprehensive picture of a country's development and well-being.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as PQLI is indeed measured by Life Expectancy at Age One.
**Option B:** This option is incorrect as PQLI is indeed measured by Infant Mortality Rate.
**Option C:** This option is incorrect as PQLI is indeed measured by Literacy Rate.

**Clinical Pearl / High-Yield Fact**
It's essential to note that the PQLI has some limitations, as it only considers three indicators and does not take into account other important factors like income, poverty, and access to healthcare. Despite these limitations, the PQLI remains a widely used and useful tool for comparing the quality of life across countries.

**Correct Answer:** D.