According to Chargaff’s rule all cellular DNAs, regardless of the species, number of adenosine residues is equal to number of thymidine residues which means that A=T; and the number of guanosine residues is equal to the number of cytidine residues; G= C. Hence that the sum of the purine residues equals the sum of the pyrimidine residues; i.e., A + G= T + C; this means that purine to pyrimidine (A+G/T+C) or pyrimidine to purine ratio (T+C/A+G) is constant for a species. So, the correct answer is option B.