A: Manhattan, New York, New York, United States
In 1950 Austrian-American biochemist Erwin Chargaff of Columbia University reported his observation from analyses of different DNAs that DNA from any cell of all organisms should have a 1:1 ratio of pyrimidine and purine bases and, more specifically, that the amount of guanine is equal to cytosine and the amount of adenine is equal to thymine (base pair equality). Watson and Crick's model of the structure of DNA confirmed Chargaff's Rules.
Chargaff, "Chemical Specificity of Nucleic Acids and the Mechanism of their Enzymatic Degradation," Experimenta (Basel) 6 (1950) 201-9.