After the bases of DNA were identified, Erwin Chargaff analyzed the percentages of adenine, thymine, guanine, and cytosine in the DNA of many different organisms. This table shows the percentages of A, T, G, and C for a human, a bacterium, and a fish. Chargaff observed an approximate rule about these percentages in all of his samples: What is the rule?

A.
A + T = G + C

B.
A = G; T = C

C.
A = C; T = G

D.
A = T; G = C