Explanation:

The Human Development Index (HDI) is a statistic composite index of life expectancy, education, and per capita income indicators, which are used to rank countries into four tiers of human development. It was developed by Pakistani economist Mahbub ul Haq. It is used to measure a country's development by the United Nations Development Programme (UNDP).

• The HDI is the geometric mean of normalized indices for each of the three dimensions. The health dimension is assessed by life expectancy at birth; the education dimension is measured by mean of years of schooling for adults aged 25 years and more and expected years of schooling for children of school entering age. The standard of living dimension is measured by gross national income per capita. The HDI uses the logarithm of income, to reflect the diminishing importance of income with increasing GNI. The scores for the three HDI dimension indices are then aggregated into a composite index using geometric mean. Hence option (a) is the correct answer.
• The HDI simplifies and captures only part of what human development entails. It does not reflect on inequalities, poverty, human security, empowerment, etc. The Human Development Report Office (HDRO) offers the other composite indices as broader proxy on some of the key issues of human development, inequality, gender disparity and poverty.