Which structural characteristic is seen in RNA but not in DNA?

A. Double strands

B. A single strand

C. Chains of nucleotides

D. A helical shape

To determine the structural characteristic that is seen in RNA but not in DNA, let's analyze each option step by step.

1. Option A: Double strands

2. Option B: A single strand

3. Option C: Chains of nucleotides

4. Option D: A helical shape

From the analysis, the correct answer is:

B. A single strand

This is the structural characteristic that is seen in RNA but not in DNA.