、阅读理解（本大题共5小题，共0分）

　　A

　　Studying carbon atoms (碳原子) locked up in tooth enamel (珐琅质), two researchers argue against the widely held belief that hominids ate little more than fruits and leaves. Sponheimer and Julia Lee-Thorp of the University of Cape Town, South Africa, report their findings in Friday's Science.

　　There aren't many,clues for us to know the life of early hominids. The shape of hominids' teeth offered the first clues. Large and flatedged with thick enamel, they looked perfect for eating nuts and fruits, different from the sharp teeth one would want to tear into meat with. The first stone tools, which would help in eating meat, didn't appear until about half a million years later.

　　Scientists have also found marks on hominids' teeth with patterns very similar to those on the teeth of modernday fruit eaters. Sponheimer and Lee-Thorp tried a new method, looking at the chemical composition of the tooth enamel. They studied the enamel for the carbon-13. Animals that eat grasses have higher carbon-13 levels than those eating fruits and other plants.

　　What they found was that the teeth of the hominids had an in-between amount of carbon-13, which meant not only they were eating fruits, they were eating a lot of grasses, or animals eating grasses. The lower carbon-13 levels could also come from eating certain types of insects (昆虫).

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