Erwin Chargaff discovered that in a DNA molecule, the number of purines always equals the number of pyrimidines. Which of the following base pairs correctly represents a purine-pyrimidine pair?

• A. Adenine (A) - Guanine (G)
• B. Cytosine (C) - Thymine (T)
• C. Adenine (A) - Cytosine (C)
• D. Guanine (G) - Cytosine (C)

Answer: (D)