Select the phrases that accurately describe properties of the most common form of the DNA double helix. There is more than one correct answer. Select all that apply. DNA contains equal amounts of adenine and thymine, and equal amounts of cytosine and guanine. A helical turn consists of about 10 nucleotides. Base pairs have a spacing of 20 A. The phosphodiester bonds between nucleotide residues run in opposite directions in the two strands. The nitrogenous bases are exposed to the solvent, whereas the sugar-phosphate backbone of each nucleotide strand is on the interior of the double helix.

A strand of DNA comprises pyrimidines, that is, cytosine and thymine and purines, that is, adenine and guanine. Of these pairing takes place between thymine and adenine and guanine and cytosine. Thus, it can be said that in DNA, the amount of adenine is corresponding to thymine, and the concentration of guanine is corresponding to cytosine. Hence, the given first statement is correct.  

DNA gives an appearance of a helical structure, in which each of the helices comprises approximately 10 nucleotides within them. Hence, the given second statement is also correct.  

The strands of DNA found in a helical structure are complementary to each other, or it can also be stated that the nucleotides present in one strand of the DNA are found in opposite direction and orientation with respect to the second strand of the DNA. The phosphodiester bonds play an essential function in combining a molecule of sugar of one nucleotide with the molecule of phosphate of the adjacent nucleotide. Hence, the given fourth statement is also correct.  

i think the answer is b.