Explanation:

The Human Development Index (HDI) is a composite index that measures average achievement in three basic dimensions of human development: a long and healthy life, knowledge, and a decent standard of living. \nOption A: 'Life expectancy at birth' is a measure of a long and healthy life, and 'Adult Literacy rate' (along with Gross Enrolment Ratio) is a measure of knowledge. These are indeed core components of the HDI. Therefore, this option is correct. \nOption B: 'Infant mortality rate' is an indicator of health but not a direct component of HDI. 'National income' (specifically Gross National Income per capita) is a component, but paired with an incorrect one. \nOption C: 'Population growth' and 'Population density' are demographic indicators but are not used in the calculation of the HDI. They relate to population distribution and change, not directly to human development achievement as defined by HDI. \nOption D: 'Sex ratio' and 'Fertility rate' are also demographic indicators. While they reflect aspects of societal well-being and reproductive health, they are not direct components used in the calculation of the HDI.