Adult birds typically retain only one functional____________?
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Answer: B. Ovary
Explanation
Adult female birds typically retain only the left ovary as an evolutionary adaptation. This anatomical reduction minimizes body weight significantly to facilitate efficient powered flight. The right ovary and oviduct regress entirely during normal embryonic development in most birds. Avian anatomy features numerous adaptations designed to reduce weight for aerial locomotion. Reproductive organs in female birds are paired during early embryonic stages before asymmetrical regression. The single functional left ovary produces eggs that pass through the left oviduct before laying.
Flight requires high metabolic efficiency and minimized body mass to generate lift successfully. Ornithologists study these unique skeletal and visceral adaptations to understand avian evolution. Some raptors occasionally show traces of the right reproductive system, though it remains nonfunctional. Option A is wrong because birds retain paired ureters for excreting nitrogenous waste. Option C is incorrect because birds have paired lungs supplemented by extensive air sacs. Option D fails because male birds retain both functional testes rather than reducing them.
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