What distinguishes a hairpin structure from a stem loop in RNA?

• A. Hairpins are double-stranded, while stem loops are single-stranded.
• B. Stem loops are found only in DNA, not RNA.
• C. Stem loops are formed by more than 10 nucleotides, while hairpins are formed by 5 to 10 nucleotides.
• D. Hairpins are longer than stem loops.

Answer: (C)