"The Hershey and Chase experiments involved the preparation of two different types of radioactively labeled phage. Which of the following best explains why two preparations were required?"

A. The bacteriophage used in the experiments was a T2 phage.
B. It was necessary that each of the two phage components, DNA and protein, be identifiable upon recovery at the end of the experiment.
C. Each scientist had his own method for labeling phage, so each conducted the same experiment using a different isotope.
D. Establishing the identity of the genetic material required observation of two phage generations.

Explanation:

It was necessary that each of the two phage components, DNA and protein also , be identifiable while recovery at the end of the experiment.

Because it was concluded that the  those component associated with bacteria by the end of the experiment must be the genetic material, it was critical that the those  component be identifiable as either DNA or protein. If it is not identifiable, then  Hershey and Chase were not be able to define the genetic material.

the rocks are classified by the geological process they are formed by. the three main groups of rocks are igneous, metamorphic, and sedimentary. minerals are not they are classified under the chemical classes they are in. these groups include silicates, sulfates and carbonates.