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