DNA is often described as having a shape like a spiral staircase. Which of the spiral staircases in the photos below is the better analogous representation of a DNA molecule? 
Definitions:
Lactase
An enzyme in the small intestine that enables humans to assimilate lactose (milk sugar).
Melanin
A pigment found in most organisms, responsible for coloration of the skin, hair, and eyes, and protection against UV radiation.
Vitamin D
A fat-soluble vitamin essential for healthy bones and immune function, obtained from sunlight exposure, food, and supplements.
Lactose Intolerance
The inability to fully digest lactose, a sugar found in milk and dairy products, leading to digestive problems.
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