About DNA, true is:

DNA 2 strands are held together by hydrogen bonds. There are covalent bonds (3'-5' phosphodiester bonds) in sugar-phosphate backbone. Melting point of DNA is closely related to the cytosine-guanine content of DNA as C & G have 3 bonds, as compared to the 2 bonds present between A & T. Most common DNA is B- DNA. A single turn of B-DNA about the long axis of the molecule contains 10 bp. The distance spanned by one turn of B-DNA is 3.4 nm (34 Ao). The width (helical diameter) of the double helix in B-DNA is 2 nm (20Ao).