Which of the following experimental steps permitted Hershey and Chase to verify that the transforming agent in a bacteriophage is DNA as well?

A. Phage particles were mixed with and permitted to infect bacterial cells.

B. The original phage coats were sheared off the surface of the bacterial cells after the initial infection therefore allowing for the "isolation" of phage DNA within the bacterial cell.

C. A mixture of phage particles and bacterial cells were injected into mice.

D. All of the above