Answer:
B. People climbing the staircase will step on the pairs of bases.
Step-by-step explanation:
DNA is a double-stranded molecule which have helical form. These two strands are joined together by the formation of hydrogen bond between two nucleotides which is complementary to each other and are present on opposite strands of DNA.
So according to this model, the bases will act as the steps of the staircase which will help the people to climb the spiral staircase that represents the DNA. So People climbing the staircase will step on the pairs of bases is the design that I would accept.