According to the passage, Garibaldi determined which of the following? A. That serum iron is produced through microbial synthesis B. That microbial synthesis of siderophores in warm-blooded animals is more efficient at higher temperatures. C. That only iron bound to other substances can be used by bacteria. D. That there is a relationship between the synthesis of siderophores in bacteria of the genus Salmonella and environmental temperature. E. That bacteria of the genus Salmonella require iron as a nutrient.