Explanation
The correct answer is A: 20 Angstrom.
The distance between two strands of DNA is known as the "major groove" and "minor groove" of the DNA double helix. The major groove is approximately 20 Angstroms wide, while the minor groove is approximately 12 Angstroms wide.
Option B (34 Angstrom) is not correct because it is a larger distance than the major groove of the DNA double helix.
Option C (3.4 Angstrom) is the distance between consecutive base pairs along the same strand of DNA, but it is not the distance between two strands of DNA.
Option D (340 Angstrom) is a much larger distance than the major groove of the DNA double helix and is not related to the structure of DNA.
