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  3. Hitherto, there is no evidence yet that would definitively prove whether or not some dinosaurs were warm-blooded, but sci

Hitherto, there is no evidence yet that would definitively prove whether or not some dinosaurs were warm-blooded, but sci

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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.
The author refers to "external mechanisms" primarily in order to
选项 A、suggest that a biochemical analysis of dinosaur thermoregulation might be a waste of time
B、suggest that other means than warm-bloodedness may account for evidence of dinosaur thermoregulation
C、explain why scientists are interested in looking for an absence of seasonal variations in oxygen 18 traces
D、suggest that metabolic rates, not warm-bloodedness, may have been the key factor in certain dinosaurs’ survival
E、imply that other factors beside temperature may dictate the ratio of oxygen isotopes
答案B
解析
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