Which of the following ratios does not change in DNA?

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.