Concept:Lower invertebrates like sponges lack specialized respiratory organs and rely on direct gas exchange through their body surface.Explanation:Sponges are simple aquatic animals with pores and canals. Their cells are in direct contact with water. Oxygen dissolved in water diffuses into cells, and carbon dioxide diffuses out. This occurs across the entire body surface. No gills, cuticle, or tracheal tubes are involved. Other animals like earthworms use moist cuticle, insects use tracheal tubes, and many aquatic arthropods and molluscs use gills.Answer:B. simple diffusion over their entire body surfaces
