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  3. Hitherto, there is no evidence yet that would definitively prove whet

Hitherto, there is no evidence yet that would definitively prove whet

游客2025-02-22  23
问题            Hitherto, there is no evidence yet that would definitively prove whether or
       not some dinosaurs were warm-blooded, but scientists have begun to investigate
       oxygen isotopic abundances in the annual growth bands of teeth or bones of high
Line    latitude, hence seasonally influenced, terrestrial dinosaurs. The ratio of oxygen
(5)     isotopes depends on temperature, and an absence of seasonal variations in
       oxygen 18—a heavy version of the common oxygen 16 atom-would strongly
       suggest that the animals maintained a constant internal temperatures. Such a
       finding would not, however, constitute "proof" that dinosaurs were warm
       blooded, as there are external mechanisms that cold-blooded animals employ to
(10)    regulate body temperatures and thereby influence metabolic rates. More
       nettlesome is that proof would have to come from discovery of intact dinosaur
       remains in which the soft tissue had not been replaced or altered, and from
       which the biomolecules responsible for thermoregulation could be extracted,
       identified and characterized. Such a proof is unlikely, as it would require an
(15)    almost impossible level of preservation over 65 million years, plus the advent of
       biotechnology that does not yet exist. [br] According to the passage, the most severe problem currently facing scientists in conclusively determining whether certain dinosaurs were warm-blooded is
选项 A、proving that thermoregulation is the primary means by which metabolic rates are influenced
B、developing a way of distinguishing between oxygen 18 and oxygen 16
C、showing that an absence of seasonal variation in oxygen 16 implies a constant internal temperature
D、finding a sample of dinosaur tissue which has survived 65 million years in a relatively intact form
E、determining which species of dinosaurs were most likely to be warm-blooded, and focusing research there
答案 D
解析
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