HDI Measures Life Expectancy, Education, and Income

Steps:

• Identify HDI's three dimensions: health (life expectancy), education (mean and expected years of schooling), and standard of living (GNI per capita).
• Examine education dimension: it uses average years of schooling completed by adults.
• Compare choices: D directly matches mean years of schooling in HDI formula.
• Confirm via official UN definition: HDI aggregates these specific indicators only.

Why D is correct:

• HDI's education index incorporates mean years of schooling as a key metric in its geometric mean formula.

Why the others are wrong:

• A: Adult literacy rate contributes to other indices like the Multidimensional Poverty Index, not core HDI.
• B: Doctors per 1000 people measures healthcare access but HDI uses life expectancy at birth for health.
• C: Unemployment rate reflects labor markets but HDI assesses income via GNI per capita logarithm.

Final answer: D