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

analyze the map below and answer the question that follows.

what does the map above tell us about the endemity of typhoid fever?

a.

there is greater occurrence of the disease in the western hemisphere.

b.

there is greater occurance of the disease in the northern hemisphere.

c.

countries located in equatorial regions are more likely to have incidents of typhoid fever.

d.

typhoid fever is more rampant among caucasian populations.