Okay, let's tackle this question about the Human Development Index (HDI). The user provided the definition from K.Park's book, so I need to make sure the explanation aligns with that. The question is likely asking which option correctly states the components of HDI.

First, the core concept here is the definition of HDI. The user's definition mentions three dimensions: longevity (life expectancy at birth), knowledge (adult literacy rate and mean years of schooling), and income (real GDP per capita in PPP USD). So, I need to confirm that the correct answer includes these three components.

Now, the correct answer should be the one that accurately lists these three dimensions. The other options would probably miss one or more components or include incorrect ones. For example, some might confuse HDI with other indices like the Human Poverty Index (HPI) which includes different indicators.

For the incorrect options, common mistakes might be including education as a separate dimension instead of combining literacy and schooling, or using GDP without specifying PPP, or adding other factors like health expenditure. Each of these would be wrong because they don't match the exact components listed in the definition.

The clinical pearl here is to remember the three pillars of HDI: life expectancy, education (both literacy and schooling), and income adjusted for PPP. A mnemonic could help, like "Live Learn Earn" to remember the three dimensions.

Finally, the correct answer is the one that lists all three components as given in the question. The user needs to ensure that their answer includes all three and matches the exact phrasing from the reference.

**Core Concept**
The Human Development Index (HDI) is a composite statistic measuring average achievement in three basic dimensions of human development: **life expectancy** (health), **education** (literacy and schooling), and **standard of living** (income adjusted for purchasing power parity). It is a key metric in the United Nations Development Programme’s Human Development Reports.

**Why the Correct Answer is Right**
The HDI integrates **life expectancy at birth** (longevity), **adult literacy rate and mean years of schooling** (knowledge), and **real GDP per capita in PPP USD** (income). These indicators collectively assess human development rather than purely economic growth. The inclusion of PPP-adjusted GDP ensures equitable comparison across countries with different cost-of-living levels.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect if it omits PPP adjustment or combines literacy/schooling incorrectly.
**Option B:** Incorrect if it replaces literacy with "enrollment rates" or uses nominal GDP instead of PPP.
**Option C:** Incorrect if it adds extraneous indicators like infant mortality or health expenditure.

**Clinical Pearl / High-Yield Fact**
Remember the HDI’s three pillars: **Live (health), Learn (education), Live Well (income)**. Always ensure GDP is adjusted for PPP (purchasing power parity) to avoid misrepresenting economic disparities.

**Correct Answer: C. Composite index combining life expectancy, education (literacy + schooling), and PPP GDP per capita**

✓ Correct Answer: D. Per capita income