Give a scientific reason: Having a flat body is an advantage among flatworms.

(N/A) $\rightarrow$ Flatworms lack specialized circulatory and respiratory systems.
The flat body shape ensures that each cell remains in close proximity to the external environment,facilitating the diffusion of respiratory gases.
Additionally,being close to the digestive tract allows for efficient nutrient distribution.
In the case of tapeworms,the digestive system is entirely absent,and nutrients are absorbed directly through the body surface,which is made possible by their flattened morphology.