SECTION 3 Directions: Each passage in this group is followed by questions based on its content. After reading a passage, choose the best answer to each question. Answer all questions following a passage on the basis of what is stated or implied in the passage. 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 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's primary purpose is to