Bacteriophages are viruses that infect bacteria. In an experiment, bacterial phages were labeled with either radioactive phosphorus or radioactive sulfur. The labeled bacteriophages were incubated with bacteria for a brief amount of time and then removed. Infected bacteria cells are found to contain significant amount of radioactive phosphorus but not radioactive sulfur. Based on the results of the experiment which of the following types of molecules in the bacterial phages most likely inject into the bacteria cells