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第一段
1 .Now listen to part of a lecture on the topic you just read about.
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第二段
1 .As much as we would like to have the remains of actual dinosaur tissue, there are sound reasons for being skeptical of the identifications made in the reading.
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第三段
1 .First, the soft, flexible substance inside the bone channels isn't necessarily the remains of blood vessels.
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2 .It is much more likely to be something else.
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3 .Like what? You might say.
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4 .Well, long after an organism is died, bacteria sometimes colonize hollows, empty areas in bones, like the other channels that once held blood vessels.
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5 .When bacteria lived inside bones, they often leave behind traces of organic material.
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6 .What the researchers in the reading are identifying as blood vessels might just be traces of soft and moist residue left by bacterial colonies.
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第四段
1 .All right. What about the iron-filled spheres?
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2 .Well, the problem is that scientists found identical reddish spheres in fossils of other animals found in the same place.
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3 .That includes fossils of primitive animals that did not have any red blood cells when they were alive.
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4 .Clearly, if these spheres appear in organisms that did not have any red blood cells, then the spheres cannot be the remains of red blood cells.
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5 .The spheres probably have a very different origin.
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6 .They are probably just pieces of reddish mineral.
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第五段
1 .Third, the collagen.
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2 .The problem is that we have never found collagen in animal remains that are older than one hundred thousand years.
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3 .Collagen probably cannot last longer than that.
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4 .Finding collagen from an animal that lived seventy million years ago would really contradict our ideas about how long collagen can last.
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5 .It is just too improbable.
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6 .The most likely explanation for the presence of the collagen is that it doesn't come from the T.rex, but from another much more recent source.
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7 .For example, human skin contains collagen, so the collagen may have come from the skin of the researchers who are handling the bone.
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