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Question
As oxygen appeared in the atmosphere, ________ also accumulated, which formed a protective barrier that protects the Earth from ________.A) ozone / UV radiation
B) elemental sulfur / volcanism
C) ferrous iron / hydroxylating radicals
D) sulfate / hydrogen sulfide
Answer
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Which of the following statements about chlamydial infections is TRUE?
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B) prevalence / mortality
C) mortality / morbidity
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Cholera is an example of a pandemic disease that
A) has multiple wild animal reservoirs and is thus difficult to eradicate.
B) spreads from a common source and could be controlled with adequate clean water and waste sanitation measures.
C) is spread through direct contact and has only a human reservoir.
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A) clonal anergy
B) clonal deletion
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A) one
B) two
C) four
D) six