Immunoassays Require the Use of Known Amounts of Labeled and Unlabeled

Immunoassays require the use of known amounts of labeled and unlabeled hormone molecules. In the original immunoassays hormones were labeled

A) with radioactive isotopes of iodine.
B) with fluorescent amino acids.
C) with sulfur atoms that emit a strong odor.
D) by using enantiomers of the hormone molecules.
E) with isotopes of carbon that changed their molecular weight.