[单选题]
The graph below shows the results of an
cud)afgu uq:h,r*c 67 experiment conducted by a team
/ nrorbm ((1ot of researchers investigating the relationship between the composition and melting point of different DNA samples. At the melting point, the DNA double helix separat
1b((ron rt /omes into two individual strands.
Two DNA samples were compared, one consisting of only PQ pairs and another one consisting of only RS pairs. Letters P, Q, R and S represent different nitrogenous bases found in the DNA.
Based on the results presented in the graph, and your knowledge of nucleotide base pairing (between purines and pyrimidines), deduce which nitrogenous bases correspond to the letters P, Q, R and S.