How Did Albert Kossel Contribute to Our Understanding of DNA

How did Albert Kossel contribute to our understanding of DNA?

A) Used X-ray diffraction to examine the structure of DNA
B) Determined that DNA contains four different nitrogenous bases
C) Found that "the transforming principle" is destroyed by enzymes that hydrolyze DNA
D) Found that the phosphorus-containing components are the genetic material of phages
E) Discovered "the transforming principle" that could genetically alter bacteria