The body of a tadpole can change shape to improve swimming speed when in danger. Which of these best explains how tadpoles developed this ability?
A. Tadpoles changed their genes in the presence of predators.
B. Tadpoles obtained chemicals from the pond water to change shape.
C. Tadpoles acquired the gene for changing shape from other tadpoles.
D. Tadpoles with the gene for changing shape survived at a higher rate.