Three measures that can improve a country's social indicators (mortality, hdi, literacy).

That statement is true

Mortality refers to the amount of people who died in that country within a period of time, which is a good indicator of the nations' health.
HDI (human development index) refers to the development of Income and education within a country
Literacy refers to how many people could read in that country, which is correlated to intelligence and higher strata of education

Answer volcanic outgassing;