The correct answer is Education.
The 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 was developed by the United Nations Development Programme (UNDP) and is published annually.
The HDI is calculated as follows:
HDI = 1/3 * Life expectancy index + 1/3 * Education index + 1/3 * Income index
The Education index is calculated as follows:
Education index = (Mean years of schooling * 2/3) + (Expected years of schooling * 1/3)
Therefore, mean years of schooling and expected years of schooling contribute to the Education dimension of the HDI.
The Health dimension of the HDI is measured by life expectancy at birth. The Income dimension of the HDI is measured by gross national income per capita (GNI per capita).
Social equity is not a dimension of the HDI.