Answer:
The correct answer is b. Breathing.
Explanation:
The first main challenge of land invertebrates was to develop a respiratory system that could efficiently extract oxygen from the air. Invertebrates, such as insects, arachnids, and mollusks, did not have lungs or tracheae like vertebrates, and they had to rely on other mechanisms to breathe.
Insects, for example, developed book lungs or tracheae, which are internal tubes that bring oxygen directly to the cells. Mollusks, like snails and slugs, developed a mantle cavity that allows them to exchange gases with the air.
Breathing was a critical challenge because land invertebrates were no longer surrounded by water, which provides buoyancy and makes it easier to breathe. They had to adapt to a new environment where oxygen was scarce and needed to be extracted from the air.
