D. A and B Both
Nucleosomes are primary structural units of chromatin. It consists of DNA bound to protein histones, i.e. core of protein histones wrapped with DNA.
Histones are basic proteins rich in lysine and arginine. These positively charged amino acids interact with the negatively charged phosphate group of DNA.
There are five types of histones, H1, H2A, H2B, H3, and H4.
H1 histones are the ones least tightly bound to chromatin and are, therefore, easily removed with a salt solution, after which chromatin becomes more soluble. Nucleosomes contain four major types of histones: H2A, H2B, H3, and H4.