Question

Cnidaria and flatworms exchange gases and remove wastes by way of their:

A) open circulatory systems.B) closed circulatory systems.C) gastrovascular cavities.D) moist skin surfaces.E) respiratory and excretory systems.

Answer 1

The answer is D, moist skin surfaces.

Explanation:
Cnidaria and flatworms respirate and extreme through their skin via diffusion.