What does it mean to provide an estimate of something

Data courtesy of the un development programme 2006-2008 and world bank 2009 the chart above compares measures of development using the hdi and gdp. why might turkey rank lower in the hdi indicator even though it has a high gdp? a. turkey has a lower gdp than comparable countries in the hdi ranking. b. turkey must increase its hdi to have a higher gdp ranking. c. turkey is only compared to other european countries in gdp, not to the world, as it is in the hdi. d. turkey may struggle to provide adequate education or health care, or it may have a lower life expectancy.