Final answer:
The Human Development Index is published by the United Nations, and it considers life expectancy, educational achievement, and living standards to assess a country's development.
Step-by-step explanation:
The Human Development Index (HDI) is published by the United Nations. This means that the correct answer to the student's question is option (a) United Nations. The HDI is a comprehensive measure that takes into account various aspects of human development, such as life expectancy, education level, and standards of living, to provide an overarching view of a country's socio-economic progress. The Index is instrumental in comparing the levels of development and well-being between different nations, thereby guiding policy decisions and development interventions.