Several Different Researchers Contributed to the Study of the Structure

Several different researchers contributed to the study of the structure of DNA. What did Oswald Avery contribute?

A) X-ray crystallography was used to show DNA is a repeating helical structure
B) The percent of adenine is equal to the percent of thymine and the percent of guanine is equal to the percent of cytosine
C) There is a transforming factor that exists and can change bacteria's characteristics
D) Transformation of bacteria did not occur with the addition of DNase enzyme, suggesting DNA is the genetic material