40. Circulatory System
Gas Exchange
Multiple Choice
Multiple ChoiceWhat is the major reason that land-dwelling mammals evolved lungs rather than gills as a primary respiratory organ?
A
Gills are not as efficient as lungs in picking up oxygen.
B
Gills are too small to provide oxygen for a mammal.
C
Air has higher oxygen content than water, so gills were no longer necessary.
D
Gills work only in aquatic animals; lungs work only in terrestrial animals.
E
Protecting gas-exchange surfaces from desiccation is difficult in terrestrial environments.
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