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Answer:
According to a source:
Nitrogenous bases in the nucleotides of each strand.
Hope this helps.
The DNA double helix is held together by hydrogen bonds between the bases attached to the two strands. The DNA double helix. The two sides are the sugar-phosphate backbones, composed of alternating phosphate groups and deoxyribose sugars. The nitrogenous bases face the center of the double helix.