Answer:
All of the answer options are correct.
Step-by-step explanation:
Chargaff contributed in understanding the structure and composition of DNA with his discoveries. He discovered that purine and pyrimidine bases are in equal amounts in a DNA molecule. He also discovered that amount of Adenine base (A) is equal to amount of Thymine base (T). It means that A pairs with T. Since A is a purine and T is a pyrimidine it also implies that purine base pairs with a pyrimidine base. This conclusion can also be arrived by taking in consideration the other base pair which is G (purine) and C (pyrimidine).