From the list below select the structural properties of DNA that were known by scientists, prior to the contributions of Chargaff, Franklin, Watson, and Crick. (Check all that apply.)

A) The scientists knew that DNA was composed of nucleotides.
B) The scientists knew that nucleotides contained nitrogen-containing bases.
C) The scientists knew that there were four nucleotides: adenine, guanine, cytosine, and thymine.
D) The scientist knew that complementary nucleotides were held together by hydrogen bonds.