Which of the Following Statements Best Supports the Watson-Crick Structure

Which of the following statements best supports the Watson-Crick structure of DNA?

A) Of the DNA examined from a wide variety of sources, the adenine and cytosine contents are always equal.
B) A non-virulent Pneumococcus can be transformed to a virulent strain by the addition of DNA.
C) mRNA will hybridize with DNA.
D) Of the DNA examined from a wide variety of sources, the adenine and guanine contents are always equal.
E) The sum of the purines present in a wide variety of DNA examined is always equal to the sum of the pyrimidines present.