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 was not a country that massively built up its navy in the early 1900s? germany china united statesbritain

When volcanoes erupt, magma (hot, molten rock) rises toward the surface of the earth. as magma cools, solid rock forms. this rock contains substances from the interior of the earth. which of the following natural resources is likely to be plentiful near subduction zones where volcanic activity has occurred in the past?

Can you give an explanation of what medc and ledc are.