Answer:
The correct answer would be a double helix.
DNA (Deoxyribonucleic acid) has a double helical structure made up of two strands of DNA.
The two strands wind around each other and form a structure similar to a twisted ladder.
Both the strands have sugar-phosphate backbone whereas nitrogenous bases are present between the two strands.
The backbones are similar to the railings of the twisted ladder and nitrogenous bases are similar to the steps of the ladder.