Which substance is of great concern to scientists studying human-generated greenhouse gases, and is thought to increase such that the earth's climate will be irrevocably changed by 2020?

a) chlorofluorocarbons

b) carbon dioxide

c) methane

d) nitrous oxide

e) ozone

Which summarizes the relationship between density of an element and its distribution in earth? a. the greater an element’s density, the greater the amount of it found in the crust. b. the denser an elements is, the smaller the amount of it earth core. c. the greater an elements density, the smaller the amount of it’s found in the crust

Unlike other andean nations, chile has a relatively small population of mestizos people of european descent indians people of asian descent

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.