Why Was the Bacterial Virus That Hershey and Chase Used

Why was the bacterial virus that Hershey and Chase used a good experimental system for determining whether DNA or protein was the molecule of inheritance?

A) The virus only contained DNA and protein and it was already known that the virus only injected its inheritable material into the cells it infected.
B) The DNA portion of the virus that Hershey and Chase used was known to be naturally radioactive, but the protein portion was not radioactive.
C) Viruses only reproduce outside of cells so it is easy to isolate their molecule of inheritance.
D) The DNA of viruses has a different, easier to visualize, structure than the DNA of humans.