Answer:
The correct option is: A. Secondary
Step-by-step explanation:
The structure of the nucleic acids i.e DNA and RNA, is divided into the following levels: primary, secondary, tertiary and quaternary.
The secondary structure of the nucleic acid is responsible for the shape of that nucleic acid. It is characterized by complementary base-pairing between the two polynucleotide strands, which wraps around each other to form a double helix. The secondary structure is stabilized by hydrogen bonding.