If there is a correlation between event a and event b, which statement is true?
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a. event b took place before event a.
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b. event a gave rise to event b.
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c. event b has something in common with event a
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d. event a would not happen without event b.

Which of these would be most useful in studying the effect of germs exchanged between the new and old worlds? a. a graph showing the number of europeans between 1492 and 1600. b. a graph showing the number of native americans between 1492 and 1600. c. a primary source description of the symptoms of an unknown disease affecting native americans in 1492. o d. a primary source description of the symptoms of an unknown disease affecting europeans in 1492.