You are what you eat. This saying has provided scientists with clues（线索）about the diet of hominids- our early relatives of 3 million years ago.

　　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 flat-edged 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 modern-day 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 to 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）.

　　But there are people who understand differently. Prof. Ungar of the University of Arkansas agrees the study offers new suggestions of hominids diet, but disagrees about the suggestion that meat could explain the lower carbon-13 levels .

　　One suggestion might be true though-take good care of your teeth .In 3 million years,a scientist might be using them to figure out what you ate for dinner.

1. Which of the following can be the best title for the text?

　　 A. Protect Your Teeth     B.What the Hominid Ate

　　 C. Where the Hominid lived D. The Formation of Teeth Enamel

2. Before the two scientists' findings, most people thought that hominids______.

　 A. lived half a million years ago

　 B. ate mainly fruits and leaves

　 C. used tools to dig grass

　 D. had sharp teeth.

3. The two scientists'findings werer mainly based on the study about _____.

　 A. the shape of hominids' teeth

　 B. the teeth marks of early fruit eaters

　 C. the grasses of 3 million years ago

　 D. the make-up of the tooth enamel

4. What is it that Prof. Ungar finds doubtful?

A. Hominids possibly ate grass-eating animals.

B. Hominids probably had different diets.

C. Hominids were basically fruit- and grass-eaters.

D. Hominids had lower level of carbon-13 in the teeth.