Why Were Some Geneticists Reluctant to Accept the Idea of Nucleic

Why were some geneticists reluctant to accept the idea of nucleic acids as genetic material even after the discovery of the structure of DNA in 1953?

A) Proteins were larger than nucleic acids
B) Nucleic acids exhibit less structural variability than proteins
C) It was proven in 1871 that proteins were the source of genetic material
D) All of these
E) None of these