Respiratory structures of land animals can include which of the following: a. lungs b. skin c. gills d. both a and b

Option D

Explanation:

Animals on land get air directly from atmosphere. They need to extract it from any other sources like water animals use air dissolved in water or so.   Lungs is the most prominent and essential organ of respiratory system of organisms that directly intake oxygen from atmosphere and release carbon dioxide back into the atmosphere.

However, all amphibians and some other creatures like earthworms uses skin as respiratory organ on land. They intake air through their permeable moist skin.

Hence, option D is correct

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