Answer:
d. Between one nitrogen-containing base on a single strand of DNA and another nitrogen-containing base on the complementary strand of DNA.
Explanation:
Polymerase Chain Reaction serves to make copies of a small amount of DNA. To perform the process of replication, the sample DNA molecule must be denatured. It means that the hydrogen bonds that hold the two DNA strands of the double helix together should be broken down.
A double-stranded DNA molecule has two DNA strands. The nitrogenous base of nucleotides of one DNA strand of a helix makes hydrogen bonds with a complementary base present on the other DNA strand. Adenine base makes two hydrogen bonds with thymine base while guanine makes three hydrogen bonds with cytosine. In this way, hydrogen bonds between the complementary bases of two DNA strands hold them together in a double helix.