Viruses Are Composed Primarily of Proteins and Nucleic Acids

Viruses are composed primarily of proteins and nucleic acids. Which of the following elements could be used to track the fate of viral proteins to determine if they entered the cell?

A) Phosphate because proteins contain phosphate, but nucleic acids do not
B) Sulfur because proteins contain sulfur, but nucleic acids do not
C) Nitrogen because proteins contain nitrogen, but nucleic acids do not
D) Oxygen because proteins contain oxygen, but nucleic acids do not